SAN Fundamentals

SAN FUNDAMENTALS

Course overview

SAN fundamentals is a web-based course introducing the fundamentals of Fibre Channel storage area networks (SANs) in a vendor-neutral perspective. It includes basic information about Fibre Channel SAN terminologies, concepts, components, and topologies.

The course begins with key concepts of a SAN. It reviews SAN components and how they solve business problems. SANs are compared to the networked-attached and direct-attached storage solutions to illustrate the benefits.

The three main Fibre Channel topologies—point-to-point, arbitrated loop, and switched fabric—are covered, including the switch or fabric topology, logging in to a fabric, cascading switches, switch initialization, and zoning, as well as Fibre Channel cabling technology.

To help reinforce learning objectives, the course includes a learning check at the end of each module and a knowledge challenge at the end of the course.

Course objectives

Upon completion of this training, students should be able to:

Explain Fibre Channel SANs and components, and compare SANs to a direct-attached storage (DAS) and a network-attached storage (NAS).

Describe the Fibre Channel architecture, characteristics, and operation including naming and addressing.

Describe Fibre Channel Arbitrated Loop topology with its operation and benefits. Describe switch topology with fabric operation and zoning concepts. Describe fiber optic technology and compare Fibre Channel cabling options and

connectors

Introduction to Fibre Channel SAN: Objectives

After completing this module, you should be able to:

Define and explain a basic SAN, how it solves business problems, and the differences between direct-attached storage (DAS), network-attached storage (NAS), and storage area network (SAN).

Identify the various SAN hardware and software components.

What is a SAN?

A SAN is a high-speed (1 to 2Gb/s data transfer rates, with the future of 10Gb/s) network with heterogeneous (mixed vendor or platforms) servers accessing a common or shared pool of heterogeneous storage devices.

SAN environments provide any-to-any communication between servers and storage resources, including multiple paths.

The parts of a SAN are:

Client layer — The clients are the access point of a SAN. Server layer — The major components in this layer are the servers, the HBAs,

including the GBICs, and the software drivers that enable HBAs to communicate with the fabric layer.

Fabric layer — This is the middle layer of a SAN, the network part of a SAN, where hubs and switches tie all the cables together into a logical and physical network.

Storage layer — This is where all the data resides on the disk drives.

Storage Network Industry Association (SNIA) statement

SNIA defines a SAN as "A network whose primary purpose is the transfer of data between computer systems and storage elements, and among storage elements. A SAN consists of a

communication infrastructure which provides physical connections, and a management layer which organizes the connections, storage elements, and computer systems so that data transfer is secure and robust."

Within this definition, there is no mention of Fibre Channel. SNIA recommends using the term Fibre Channel SAN when the network is based on Fibre Channel technology.

Although a SAN typically references Fibre Channel, it can be based on other technologies such as Enterprise System Connection (ESCON) and iSCSI, which is a protocol that enables a server to access storage through an Ethernet network adapter.

For more information on SNIA, refer to the website at: http://www.snia.org

SAN history and business challenges

Historically, information technology companies have taken a segmented approach with storage. Specific servers executed specific applications, and each system was directly attached to the storage it required.

As the need for faster and bigger storage grew, users purchased more drives for their arrays or replaced older technologies with newer, faster ones.

Today, businesses are faced with several challenges:

Exponential storage growth Zero downtime requirements Convenient scheduling of downtime to add capacity

SolutionTo answer some of the challenges businesses face, SAN storage is external and can be shared without impacting system performance or the primary network. SANs provide a:

Secure implementation of storage I/O methods over network transports. High-speed, scalable, robust network of servers and storage devices. Storage service that:

Connects to servers enterprise-wide. Centralizes data. Moves data automatically for availability and replication. Provides accelerated data access. Supports advanced storage management. Provides for highly-available configurations.

Natural platform for server clustering applications.

http://www.snia.org/

SAN benefits

SAN benefits provide high return on investment (ROI) and reduce the total cost of ownership (TCO) by increasing performance, manageability, and scalability.

However, SANs are not for everyone. Sometimes the benefits do not justify the costs for small companies. A good guideline is the use of 16 servers. If you have more than 16 servers, a SAN should be beneficial.

Some key benefits of SANs are:

Reduced data center rack and floor space — Because you do not need to buy big servers with room for many disks, you can buy fewer, smaller servers, which takes less room in the data center.

Disaster recovery capabilities — SAN devices can mirror the data on the disk to another location.

Increased I/O performance — SANs operate faster than internal drives or devices attached to a LAN.

Fibre Channel SANs offers these additional benefits, which are covered in more detail on the next pages.

Performance — Distance and speed Efficiency — Reliability and nondisruptive scalability Manageability — More devices supported with less people Connectivity — Any-to-any connections Cost effectiveness — Serverless backups and tape library sharing Modular scalability — Dynamic capacity Consolidated storage — Sharing of centralized storage

Performance Distance — Fibre Channel permits hosts and devices to be connected to locations

10km (6 miles) apart. Distance capabilities are dependent on Fibre Channel cabling types which is discussed in the Fibre Channel Cabling module. Distance example:

100m (60 miles) with copper cabling (used for shorter distances) 500m with multimode fiber optic cabling (used for medium distances) 10km with singlemode fiber optic cabling (used for longer distances)

Speed — Fibre Channel permits theoretical speeds of 10Gb/s and higher with Fibre Channel cabling (five times faster than SCSI and LAN data transfers). Fibre Channel continues to evolve and enhance performance and distance characteristics.

Efficiency

Several factors contribute to the efficiencies of SANs:

Reliability — Fibre Channel transports data with a very low error rate. A bit error rate (BER) of 1 x 0 to 12 is the minimum acceptable rate.

Independent I/O operations — Typically, interfaces support only themselves. Fibre Channel supports simultaneous use of multiple interface protocols. In Fibre Channel, I/O operations are unbundled from dependence on the physical interconnections. One I/O operation can take place without waiting for another one to finish.

Online storage migration capabilities — Storage can be dynamically allocated and reallocated among hosts without interruption, resulting in improved storage usage.

Elimination of server downtime while adding storage — Using Fibre Channel-based storage, storage resources can be added or deleted without interrupting the production environment.

InefficiencyThough SANs can be very efficient, problems can still occur to make a SAN inefficient. For example:

Poor design — Improper bandwidth, latency issues, congestion Cabling problems — Inconsistent labeling practices, damaged cables, wrong cables,

signal loss, patch panel problems Unsuitable drivers — Wrong drivers, outdated drivers, driver interaction with other

software, missing drivers Untrained staff — Incomplete training, poor vendor support, pushing projects with

limited resources, no SAN team Incomplete management software — Not setting up the right alarms and

notifications, not monitoring or responding to problems

Manageability

The more complex the network, the more complex the management tasks. SAN provides the ability to combine many of these tasks under one management platform.

The complexity of installation and configuration increases as additional devices are placed within the SAN. For example:

Users require continuous connectivity and access. Servers require file security, load balancing, and storage file access. Switches are managed for system maintenance and to enhance performance. Tape libraries and backup devices require software to run and schedule the backups. Storage requires a software interface to manage redundant array of independent

disks (RAID).

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Connectivity

SANs are scalable from two to 14 million ports in one system, with multiple topology choices such as:

Point-to-point — A dedicated and direct connection exists between two SAN devices.

Arbitrated loop — SAN devices are connected in the form of a ring. Switched fabric — SAN devices are connected using a fabric switch. This enables a

SAN device to connect and communicate with multiple SAN devices simultaneously.

Cost effectiveness

Several features of Fibre Channel SANs enable cost effectiveness.

Serverless backupThis type of backup enables a direct backup from disk to tape, without going through the host that offloads data from the network. The host initiates the process, but another intelligent device can transfer the data.

Tape library sharingProviding tape drives to each server is costly, and it also involves the added administrative overhead of scheduling the tasks and managing the tape media. SANs enable greater connectivity of tape drives and tape libraries, especially at greater distances.

Data sharingSAN data sharing reduces the need to hold multiple copies of the same file or database. This reduces duplication of hardware costs to store the copies. It also enhances the ability to implement cross-enterprise applications such as e-business, which could be inhibited when multiple data copies are stored.

Server reductionsBy moving data to SAN-attached storage subsystems, the servers themselves might no longer need to be configured with native storage. In addition, the introduction of LAN-free and server-free data transfers largely eliminate server cycles to manage tasks such as backup and recovery, archive, and recall.

Modular scalability

Modular scalability provides support for an unpredictable environment, enabling changes to the infrastructure as business needs evolve.

Nondisruptive Capacity can be dynamically scaled on demand—without disrupting ongoing operations—providing maximum flexibility to accommodate business growth.

SANs enable disk storage to be scaled independently of servers.

Consolidated storage

Consolidating storage (primary and secondary) in a SAN and sharing the resource across multiple servers reduces the cost of storage management, and reduces the cost of additional hardware devices.

This diagram shows how three servers can use one storage device instead of three DAS devices that can be costly. Additional hardware and its administration would be required for each additional device.

Storage solutions

For companies to continue being successful, data storage has become a business-critical consideration. A storage solution is a fully integrated and tested storage-product configuration consisting of a combination of hardware, software, and services—all of which focus on solving specific customer business problems.

Primary storage is increasingly an important part of an enterprise information technology infrastructure. Companies continually need larger amounts of data storage.

Storage can be internal or external:

Internal storage — Internal storage consist of disks located within the host server that has a basic RAID controller. The disks themselves, in most cases, are the same as those used in external storage shelves, using SCSI and Fibre Channel technologies.

External storage — External storage connects to a physically separate storage cabinet or shelf. The interface is through an HBA located in the host server normally using a Fibre Channel interface. The similarities continue in the support of all the SCSI or Fibre Channel standards as well as optional RAID levels. External enclosures provide electrical isolation to disk units and in some cases can provide additional RAID support.

Data storage solutions are:

Direct-attached storage (DAS) Network-attached storage (NAS) Storage-attached network (SAN)

Storage solution comparison table

DAS

DAS is storage connected to a server. The storage itself can be external to the server connected by a cable to a controller with an external port, or the storage can be internal to the server. Some internal storage devices use high-availability features such as adding redundant component capabilities.

In the following diagram:

The DAS configuration starts with a server. An HBA is being installed in the server, so the server can communicate with the

external storage. A storage disk drive is installed into a storage subsystem. The server and storage are connected with cables.

NAS

NAS is storage that resides on the LAN behind the servers. NAS storage devices require special storage cabinets providing specialized file access, security, and network connectivity.

NAS

Requires network connectivity. Requires a network interface card (NIC) on the server to access the storage. Provides file-to-disk block mapping. Provides client access at the file level using network protocols. Does not require the server to have a SCSI HBA and cable for storage access. Supports FAT, NTFS, and NFS file systems.

NAS storage devices require special storage cabinets providing specialized file access, security, and network connectivity. On the server side, the SCSI HBA is no longer needed for storage access. Servers access the NAS the same way that clients do.

Clients, including servers, attach to the NAS as a share, similar to attaching shares from server-attached storage. Only the server requires a NIC to access the storage.

In this diagram, the client request (the client can be a server) is within a TCP/IP header and is forwarded to the NAS device. All block-level mapping is performed on the NAS.

Advantages

Eliminates awkward HBA and RAID controller configuration and cost Is a plug-and-play device

Accesses by any device with a network connection Supports many different operating systems that can access the NAS as long as these

devices support the file system Performs backups using NAS tape backup devices and NAS storage while using less

storage resources Provides the ability to transition from server-based storage to a SAN

DisadvantagesThe disadvantages of NAS are what led to the acceptance of SANs.

Depends on the client LAN, which makes it accessible only to devices on the LAN Limits LAN bandwidth Limits data handling capabilities Lower performance than a SAN

SANs:

Enable handling of secure massive amounts of data without having to compromise the overall performance and integrity of the network.

Successfully deal with the massive amounts of data that is stored and accessed on corporate networks.

SAN

A SAN is a network composed of many servers, connections, and storage devices, including disk, tape, and optical storage. The storage can be located far from the servers that use it.

One server or many heterogeneous servers can share a common storage device, or many different storage devices. SAN components include:

Client access to the LAN and SAN levels. Servers connected to switches or hubs that connect to storage. Storage connected to switches or hubs that connect to servers. Routers or bridges that connect and interface with tape libraries or backup devices.

A SAN is different from traditional networks because it is created from storage interfaces.

SAN solutions use a dedicated network behind the servers and are based on primarily Fibre Channel architecture.

Fibre Channel provides a highly scalable bandwidth over long distances. Fibre Channel has the ability to provide full redundancy, including switched parallel data paths to deliver high availability and high performance.

Clients with business-critical data and applications are concerned about high availability. Fibre Channel SANs help provide the no-single-point-of–failure configurations that business-critical customers require by being able to mirror data or cluster servers over a SAN.

Therefore, a SAN can avoid network bottlenecks. It supports direct, high-speed transfers between servers and storage devices in the following methods:

Server to storage— This is the traditional method of interaction with storage devices. The SAN advantage is that the same storage device can be accessed serially or concurrently by multiple servers.

Server to server —This provides high-speed, high-volume communications between servers.

Storage to storage — In this configuration of a SAN, a disk array could back up its data directly to tape across the SAN, without server processor intervention. A device could be mirrored remotely across the SAN for high-availability configurations.

Disadvantages of a SAN

Incompatibilities between vendors are not completely resolved in some implementations.

Fibre Channel RAID is expensive when compared to parallel SCSI.

Fibre Channel hardware implementations can be expensive.

Storage solution comparison table

DAS NAS SAN

Applications Any File serving Storage for application servers

Server and operating systems

General purpose Optimized General purpose

Storage devices

Internal or external dedicated

External direct-attached

External shared

Management Labor intensive Centralized Centralized

Data centers Workgroup or departmental

Workgroup or departmental

Small workgroup to enterprise data centers

Performance Network traffic Increased network performance

Higher bandwidth

Distance None Limited distances Greater distances

Speed Bottlenecks Improved bottlenecks

Greater speeds

High availability

Limited Limited Offers no-single-point-of-failure storage and data path protection

Cost Low cost Affordable Higher cost, but greater benefits

SAN components

Fibre Channel SAN environments and components enable the development of solutions that provide high performance and high availability, which are the fundamental requirements of a storage network.

Fibre Channel devices effectively combat the problems related to bandwidth, which generally occur during bulky operations, such as backup and restore operations. Hardware components offer different features to provide for a small SAN to a high-speed and high-volume SAN data center.

A wide range of hardware and software products make up the components of a SAN. SAN components include:

Client layer

Host layer Servers HBAs

Fabric layer Hubs or switches Bridges and multiplexers Routers SAN software Fibre Channel cables

Storage layers Storage devices Backup devices

SAN servers

After the client layer, the first SAN component that enhances performance is the implementation of the SAN server.

Dataless serversData is moved from the servers to storage devices. This enables the servers to perform better because they now manage less data and can handle the server tasks.

Its the data that is important to the business. With a SAN, you can purchase fewer and smaller servers than with other topologies that rely more on the servers to manage data.

ClusteringSANs support server clustering. Clusters are a set of independent network servers working

together to provide fault tolerance. The services, applications, and resources running on any node in the cluster are available to all connected network users. Clusters are invisible to users and interact as though each were a single server.

Role of the server

Serve as the access point for the clients Provide load balancing and data caching to improve performance Schedule backups

HBAs

The next component in a SAN is the installation of the HBA in the server.

HBAs compared to NICsHBAs are similar to NICs used in LANs and other non-SAN networks. They replace the traditional SCSI cards and interconnect SAN devices, such as servers and storage devices.

An HBA provides hard-coded, 64-bit World Wide Name (WWN) and World Wide Port_Name (WWPN) addresses to a SAN device and its ports, and provides more functionality than NICs.

Role of the HBAThe HBA in the SAN provides initialization of Fibre Channel devices and ports that belong to an arbitrated loop or fabric. HBAs also provide:

Support to the upper-level protocols, such as TCP/IP, ensuring successful interaction between SANs and connected LANs.

Encoding of data as per the 8B/10B scheme, which is a fast, extremely secure, and reliable data-encoding mechanism.

Fibre Channel HBAs:

Provide gigabit technology. Can address more devices than SCSI or NIC counterparts. Provide I/O connectivity to more devices over longer distances than SCSI. Provide the ability for Fibre Channel frames to relay over gateways.

Fibre Channel hubs and switches

HubsThe hubs on a storage network are used to implement the ring-like Fibre Channel Arbitrated Loop (FC-AL) topology. Unlike the hubs used in traditional networks, a typical Fibre Channel hub can support up to 126 nodes. Hubs have 7 to 12 ports that can be used to connect devices in a Fibre Channel configuration.

SwitchesSwitches provide many more connections than hubs and are used in FC-AL and switched fabric configurations. They offer 8 to 16 ports, and a single switch alone enables the creation of a small-scale SAN. Switches offer a dedicated bandwidth of 100Mb/s and above for each port, enabling frames to be routed between SAN nodes at high speeds.

Fibre Channel switches are divided into three categories:

Loop switches — These switches are comparatively low cost. These are used to connect an FC-AL loop to the rest of the fabric.

Fabric switches — These switches are expensive and are predominantly used to implement the switched fabric topology.

Directors — This is the most expensive category of switches, but they offer the best performance and maximum reliability. The estimated annual downtime for a director is barely five minutes.

Other advanced services provided by Fibre Channel switches are:

Buffer-to-buffer flow control during transactions Services, such as:

Fabric Login (FLOGI) — Enables nodes to be successfully initialized (allocated a unique address) in a switched environment, enabling communication between two nodes

Simple Name Server (SNS) — Helps a source node to discover the destination node within the fabric without causing unnecessary communication overhead

Registered State Change Notification (RSCN) that notifies Fibre Channel nodes about the changes in the existing topology

Fibre Channel routers and gateways

Routers Fibre Channel routers provide an interface among IP-based devices, LANs, and the storage network. These devices transfer storage data between different networks by using various transmission media and addressing methods.

GatewaysFibre Channel gateways enable interconnect networks using different protocols and addressing methods over a wide area network (WAN). However, they might not be able to perform protocol conversion.

Fibre Channel bridges and multiplexers

BridgesBridges provide the ability to connect parallel SCSI devices to a Fibre Channel network. They perform a protocol conversion function between SCSI and Fibre Channel.

Note: Bridges are also referred to as Fibre Channel SCSI routers.

Parallel SCSI devices can be included in a SAN with the addition of a SCSI-Fibre Channel bridge. These parallel storage devices use original SCSI commands to enable SCSI initiators access to data blocks.

MultiplexersMultiplexers are a special category of bridges that interleave signals from multiple devices and transmit them simultaneously through a single transmission medium.

A multiplexer effectively uses the available network bandwidth.

Storage devices

Storage can be based on SCSI or Fibre Channel.

Fibre Channel-based storage enables direct connection to the Fibre Channel network, providing distance and speed enhancements over SCSI.

A SAN uses the following storage devices:

Just a Bunch of Disks (JBOD) A JBOD is a set of multiple storage disks acting as a single storage entity. Data stored on a JBOD is extended across multiple disks. JBOD data access is slow. The fault-tolerance level and reliability of JBOD is lower than what is expected from an expensive storage system.

Tape librariesThese are inexpensive storage solutions. Tape libraries store data from 10GB to several thousand terabytes of data. They also offer high reliability for backup transactions. Most vendors offer self-managing tape subsystems that makes tape libraries the ideal backup medium.

Storage drivesThese are high-availability drives that store high volumes of data. They are a reliable storage solution, providing failover capabilities.

Storage arraysThe storage array is an external drive enclosure containing a controller, power supply, fan assembly, and disk drive housings. A single array holds several drives, producing an enormous amount of storage in a compact unit. Some array components can be replaced, so that installation and replacement does not require downtime. The series of fixed disk drives are logically addressed as a single, larger drive.

Backup devices

Backup and recovery system configurations can range from an external tape drive attached to the corporate server, to large tape libraries capable of handling hundreds of backup media.

Tape librariesA tape library is a high-capacity data storage system for storing, retrieving, reading, and writing multiple magnetic tape cartridges. They meet the performance and capacity characteristics of a SAN environment.

AutoloadersAutoloaders are ideal for applications that require high-capacity, high-speed tape backup where physical space, backup time, and personnel resources are limited.

SAN Software components

SAN software is required to manage and troubleshoot a SAN environment. SAN software is used to manage:

Hardware and software within the SAN (such as storage, switches, and hubs) Multiple storage enclosures Multiple operating systems Multiple vendors Resources to be managed in different geographical locations

SAN management functions include:

Device installation, configuration, and monitoring SAN resource inventory Report utilities Automated component and fabric discovery Management of fabric configuration Name services Security management Performance monitoring and load balancing

At the storage levelSAN management includes the management of:

Disks and disk arrays

Tapes and tape libraries Cabling Hubs, switches, gateways, bridges, and routers Interswitch links HBAs

SAN software uses:

SCSI enclosure services that might impact FC-AL bandwidth Simple Network Management Protocol (SNMP)

At the enterprise levelSAN software manages:

Storage Networks Servers Desktops

SAN software uses:

Web Based Enterprise Management (WBEM) Common Interface Model (CIM) Desktop Management Interface (DMI) Java Application Management Interface (JAMI)

Introduction to Fibre Channel SAN: Learning check

1. A SAN might contain both heterogeneous servers and heterogeneous storage? Choose

the correct answer.

True

False

For help, see What is a SAN?

2. Which component is not a SAN layer? Choose the correct answer.

Client

Server

Storage

Interlinks

For help, see What is a SAN?

3. Fibre Channel permits hosts and devices to be up to 500m apart. How far can solutions span the distance? Choose the correct answer.

To over 10km

To over 20km

To over 30km

To over 40km

For help, see SAN benefits

4. Which data storage requires specific storage cabinets? Choose the correct answer.

SAN

NAS

DAS

For help, see Storage solutions

5. Which solution provides for storage units to be very far from the servers? Choose the

correct answer.

SAN

NAS

DAS


6. Which data storage solution is the traditional method of attaching storage to hosts? Choose the correct answer.

SAN

NAS

DAS


7. Which component offers high speed and can store up to several terabytes of data? Choose the correct answer.

HBA

Disk array

SAN management

SAN switch

For help, see Storage devices

8. What provides initialization to Fibre Channel devices? Choose the correct answer.

HBA

Disk array

SAN management

SAN switch

For help, see Storage components

9. What uses multiple tape drives and mechanisms to address large scale backup environments? Choose the correct answer.

Tape libraries

Optical libraries

Autoloaders

For help, see Backup devices

Fibre Channel basics: Objectives


Define Fibre Channel. List the features of Fibre Channel. Identify Fibre Channel framing protocol and how it functions. Identify how Fibre Channel ports are used. Identify Fibre Channel layers and what they represent. List the classes of service and how they relate to data transfer. Identify the naming and addressing of Fibre Channel. Define Fibre Channel basic terms. List three basic Fibre Channel topologies. Identify Fibre Channel port connections and how they interface with hubs, switches, and

other devices. Identify Fibre Channel addressing and its benefits.

What is Fibre Channel?

Industry requires an efficient and high-performance transfer of information between devices such as computers, storage devices, and other peripherals.

Fibre Channel is a multilayered network based on a series of standards from the American National Standards Institute (ANSI). These standards define characteristics and functions for moving data across the network. They include definitions of physical interfaces such as cabling, distances, and signaling; data encoding and link controls; data delivery in terms of frames, flow control, and classes of service; common services; and protocol interfaces.

With Fibre Channel:

Hosts and applications see storage devices attached to the SAN as if they are locally attached storage.

Multiple protocols and a broad range of devices can be supported. Connections can be either optical fiber (for distance) or copper cable links (for short

distance at low cost).

ProtocolsFibre Channel uses three protocols:

Point-to-point — Devices are directly connected to other devices without the use of hubs, switches, or routers.

Fibre Channel Arbitrated Loop (FC-AL) — FC-AL has a shared bandwidth, distributed topology, connects with hubs, and is the simplest form of a fabric topology.

Fibre Channel Switched Fabric (FC-SW) — FC-SW provides the highest performance and connectivity of the three topologies. It has nondisruptive scalability and switch connection.

Fibre Channel supports 126 nodes on an FC-AL, and 16 million nodes on an FC-SW and provides connectivity over several kilometers (up to 10km) when using optical fiber.

Fibre Channel features

Fibre Channel has features that include:

Price:performance — Fibre Channel expense is offset by its high-speed bandwidth benefit.

Hot pluggability — Fibre Channel drives can be installed or removed while the host system is operational. This is crucial in high-end and heavy-use server systems where there is little or no downtime.

Reliability — Fibre Channel is the most reliable form of storage communication. Multiple topologies — Customers can develop a storage network with configuration

choices at a range of price points, levels of scalability, and availability. Full suite of services — The Fibre Channel set of storage network services include

discovery, addressing, LUN zoning, failover, management, and security. Longer cable lengths — Fibre Channel maintains data integrity through long cables.

Cable lengths include:

30m between nodes with copper cabling

500m between nodes with multimode cabling and shortwave lasers

10km between nodes with single-mode cabling and longwave lasers

Gigabit bandwidth — Both 1Gb and 2Gb solutions are available and backward compatible, providing customers with the highest bandwidth network interface technology in the industry.

Loop resiliency — Fibre Channel provides high data integrity in multiple

devices (including Fibre Channel RAID) on a loop. Multiple protocols — Protocols include SCSI, IP, VI, ESCON, HIPPI, IPI, and IEEE

802.2, (refer to the Terms and Definitions section) to meet needs for storage connectivity, cluster computing, and network interconnect.

Scalability — Moving from single point-to-point gigabit links to integrated enterprises with hundreds of servers, Fibre Channel is a high-performing and flexible configuration.

Congestion-free flow — The Fibre Channel flow control delivers data as fast as the destination buffer is able to receive it for high throughput data transfers. This enables backup, restore, remote replication, and other applications to run more efficiently.

Fibre Channel applications High-performance storage High-performance disk and tape I/O Large databases and data warehouses Storage backup systems and recovery Server clusters Network-based storage High-performance Workgroups Campus backbones Digital audio and video Networks

Framing protocol

Framing protocol is a communication procedure that:

Accepts data and divides it into frames for transmission. Reassembles the received frames into a packet for delivery to a receiving device. Positions the data in the frames for improved performance and hardware efficiency.

A frame is a string of data bytes, prefixed by a start of frame (SOF) delimiter and followed by an end of frame (EOF) delimiter.

Frame specifications

2148-byte maximum frame size 4-byte SOF 24-byte header (destination and source

addressing control fields) 0 to 2112-byte data 4-byte cyclic redundancy check (CRC) 4-byte EOF

Fibre Channel ports

On a computer or communication device, a port is a specific place for being physically connected to some other device, usually with a socket and plug of some kind. A port is also a logical connection place and specifically, using a protocol, the way a client program specifies a particular server program on a computer in a network.

A node is a connection point. It is either a redistribution point or an end point for data transmissions. In general, a node has programmed or engineered capability to recognize and process or forward transmissions to other nodes. A node can be a server or storage system, a tape backup device, or a video display terminal. Each node must hold at least one port for providing access to other devices.

Fibre Channel ports

Fibre Channel description

N_port All node (server or storage) ports are called N_Ports. An N_Port attaches to an F_Port in a point-to-point protocol. N-port to N-port is uncommon, so when two nodes are direct-attached it is through an arbitrated loop (NL_Port to NL_Port).

L_port All loop-hub ports are called L_Ports, which stands for loop ports.

NL_port An N_Port that contains arbitrated loop functions associated with arbitrated loop topology is called an NL_Port.

F_port The F_Port, or fabric port, is the Link_Control_Facility within the fabric (switch) that attaches to an N_Port.

FL_port An F_Port, that contains arbitrated loop functions associated with arbitrated loop topology is called an FL_Port, which stands for fabric loop port.

E_port An E_Port is used for connecting fabrics (switches). The link is called the inter-switch link (ISL).

G_port A G_Port (generic port) can auto-discover its type. It automatically configures itself as an E, N, or NL port.

Switch ports

Switch ports become a port type depending on what gets plugged into them.

Switch ports are usually G_Ports when nothing is plugged into them. If you plug a host port into the switch, it becomes an F_Port. If you plug a switch into a fabric switch, it becomes an E_Port. Plug a hub into a switch port and it becomes an FL_Port. Plug a host port into a FL_Port and it becomes an NL_Port. The diagram shows how port names change depending on what devices are

connected.

Fibre Channel layers

Fibre Channel consists of multiple layers similar to the Open Systems Interconnect (OSI) layers in network protocols. These layers communicate instructions for transmitting data.

The functions of each layer are:

Node level Upper-level protocol (ULP) — Provides the communication path for the

operating system, drivers, and software applications over Fibre Channel FC-4 — Defines the mapping of the ULP to the Fibre Channel FC-3 — Provides common services for multiple ports on a Fibre Channel

node Port level

FC-2 — Transfers frame formats, performs sequence and exchange management, controls the flow of data, and administers the topologies

FC-1 — Encodes and decodes data to transmit it through a physical media FC-0 — Acts as an interface for the physical media

Layer FC-4

The upper-layer protocol mapping FC-4 defines the mapping of the ULP to the other Fibre Channel levels. It includes application protocols, such as SCSI-3, IP, HPPI, and single-byte command code sets (SBCCS) or rules.

The SBCCS transforms data into Fibre Channel frames and back again. Mapping rules provide clear instructions between ULP and the FC-3 and FC-2 levels to enhance interoperability among applications.

Layer FC-3

FC-3 provides common services for multiple ports on a Fibre Channel node.

The FC-3 level manages login information for all nodes and ports. Each port on the FC-3 level knows which ports are busy and why. Knowing which ports are busy enables the FC-3 level to route frames between two N_Ports.

The FC-3 level is unaware of the topology of Fibre Channel or the signaling at the lower levels. This is handled by FC-1 and FC-2 levels.

Layer FC-2

The FC-2 is the framing and signaling protocol that transfers frame formats, performs sequence and exchange management, controls the flow of data, and administers the topologies. Its responsibility is the process of moving frames between ports. This protocol is concerned with the construction and management of frames, sequences, and exchanges.

Layer FC-1

FC-1 encodes and decodes data to transmit it through a physical media. It provides an 8-bit byte to 10-bit byte character encoding scheme.

This scheme converts an 8-bit byte into two 10-bit characters that are used to balance ones and zeros in a high-speed data transfer system.

Layer FC-0

FC-0 is the physical interface for cables, connectors, and transceivers. It provides signaling, media, receiver, and transmitter specifications.

Framing classes of service

Fibre Channel defines several communication systems called classes of service. The selection of a class of service depends on the type of data being transmitted.

Class 1Class 2Class 3Class 4 and 6

The following table summarizes the classes of service in Fibre Channel.

Class of service

Fibre Channel description

Class 1 Dedicated connection In-order delivery, acknowledge first frame only

No flow control after first frame of connection

Class 2 Connectionless Frame switched Out-of-order delivery possible Acknowledge each frame

Buffer-to-buffer and end-to-end flow control for all frames

Class 3 Frame switched Out-of-order delivery possible No acknowledgments

Buffer-to-buffer frame control for all frames

Class 4 Connection oriented Virtual circuit

In-order delivery

Class 5

Reserved

Class 6 Connection oriented

Multicast service

Class 1

Class 1 service establishes a dedicated connection. This connection is established, retained, and guaranteed by the fabric. The maximum bandwidth available between the communication points is committed to the connection and is maintained as long as the circuit remains.

Because the connection is guaranteed, no interruptions are tolerated and the frames can be delivered in the same order as they are transmitted. If the fabric is not a part of this implementation of Class 1 service, the connection is treated as a special form of point-to-point protocol.

Features

Dedicated connection Frame delivery acknowledgement Constant circuit and full bandwidth Frame arrival in order Costly, not widely implemented

Class 2

Class 2 service does not guarantee the delivery of the frames in the same order as they were transmitted. The circuit is not dedicated. This class of service is connectionless. However, it provides for the reassembly of the frames at the receiver, acknowledgement of data frame retrieval, and notification of any transmission errors.

Features

No dedicated connection required Acknowledgement of frame delivery provided Frames can arrive out of order In-order delivery can be requested during login Notification of nondelivery of frames

Class 3

Class 3 supports unacknowledged delivery of data frames. Receiving N_Ports do not acknowledge receipt of valid data frames. Any recovery from errors or acknowledgement of successful data transmission is the responsibility of the ULP.

It is the responsibility of the fabric to make a best effort to deliver frames to the intended destination, but does not issue a busy or reject frame if it is unable to make delivery to the destination N_Port.

Features

Connectionless Nonnotification of delivery Error recovery provided by ULPs Low overhead and high performance Used in loop environments

Classes 4 and 6

These two services are not widely implemented.

Class 4:

Defines virtual circuits. Is connection oriented. Allows for the assignment of fractional

bandwidth to virtual circuits. Allows for the assignment of different

quality of service parameters.

Class 6:

Multicast originator sends a single transmission to multiple destinations.

A multicast server accumulates responses. A multicast server sends a single

response.

Naming and addressing

Each node has a fixed 64-bit worldwide name (WWN) assigned by the manufacturer. The address can be considered analogous to a media access control (MAC) address. This guarantees uniqueness within a large, switched networked.

Unlike the MAC address, the WWN is not used to transport frames across the network.

Two WWNs are assigned:

The N_Port node WWN is assigned for the HBA. The N_Port has a WWN assigned for each port on the HBA.

Terms and definitions

The following terms are frequently used in Fibre Channel technology:

802.2 — The IEEE logical link control layer of the OSI model. Acknowledgement frame (ACK) — Used for end-to-end flow control. An ACK is sent

to verify receipt of one or more frames in Class 1 and Class 2 services. Arbitrated Loop Physical Address (AL_PA) — A 1-byte value used in the Arbitrated

Loop topology used to identify L_Ports. This value will then also become the last byte of the address identifier for each public L_Port on the loop.

Arbitrated loop — One of the three Fibre Channel topologies. Up to 126 NL_Ports and one FL_Port are configured in a unidirectional loop. Ports arbitrate for access to the loop based on their AL_PA. Ports with lower AL_PAs have higher priority than those with higher AL_PAs.

Buffer-to-buffer credit (BB_Credit) — Used for buffer-to-buffer flow control which determines the number of frame buffers available in the port it is attached to.

Close primitive signal (CLS) — Applies only to the Arbitrated Loop topology. It is sent by an L_Port, which is currently communicating on the loop to close communication with the other L_Port.

End of frame (EOF) delimiter — An ordered set that is always the last transmission word of a frame. It is used to indicate that a frame has ended and indicates whether the frame is valid.

ESCON — Enterprise Systems Connection, a type of fiber jumper. Fabric — A set of one or more connected Fibre Channel switches acting as a Fibre

Channel network. Fiber optic (or optical fiber) — The medium and technology associated with the

transmission of information as light impulses along a glass or plastic wire or fiber.

Frame — The basic unit of communication between two N_Ports. Frames are composed of a starting delimiter (SOF), a header, the payload, the cyclic redundancy check (CRC), and an ending delimiter (EOF).

HIPPI — High-Performance Parallel Interface standards. IEEE — Institute of Electrical and Electronics Engineers standards. IP — Internet Protocol. Link — Two adjacent unidirectional fibers (signal lines) transmitting in opposite

directions, using their associated transmitters and receivers. The pair of fibers can be copper electrical wires (differential pairs) or optical strands. One fiber sends data out of the port and the other fiber receives data into the port.

Link service — A facility used between an N_Port and a fabric or between two N_Ports. Link services are used for such purposes as login, sequence and exchange management, and maintaining connections.

Node — A server, storage system, tape backup device, or video display terminal. Any source or destination of transmitted data is a node. Each node must hold at least one port for providing access to other devices.

Nonparticipating mode — Where an L_Port enters the nonparticipating mode if more than 127 devices are on a loop and it cannot acquire an AL_PA. An L_Port can also voluntarily enter the nonparticipating mode if it is still physically connected to the loop, but does not participate. An L_Port in the nonparticipating mode cannot generate transmission words on the loop and can only retransmit words received on its inbound fiber.

Ordered set — A 4-byte transmission word, which has a special character as its first transmission character. An ordered set can be a frame delimiter, primitive signal, or primitive sequence. Ordered sets are used to distinguish Fibre Channel control information from data.

Originator — An N_Port that originates an exchange. Participating mode — A normal operating mode for an L_Port on a loop. An L_Port in

this mode has acquired an AL_PA and is capable of communicating on the loop. Port — The connector and supporting logic for one end of a Fibre Channel link. Primitive sequence — An ordered set transmitted repeatedly and used to establish

and maintain a link. Primitive signal — An ordered set used to indicate an event. Private loop — An arbitrated loop that stands on its own. It is not connected to a fabric. Protocol —In a Fibre Channel SAN, a data transmission convention encompassing

timing, control, formatting, and data representation. Public loop — An arbitrated loop connected to a fabric. Responder — Where the N_Port is the exchange that the originator communicates

with. SAN — One or more Fibre Channel fabrics used to connect storage systems, servers,

and management appliances. Typical SANs have one fabric (for environments where moderate data availability is required), two fabrics (when redundancy is required in the storage networks), or even three or more fabrics (when an extremely large number of ports is required). Use caution with the terms fabric and SAN because many SANs have two redundant fabrics.

SCSI — Small Computer System Interface. Sequence — A group of related frames transmitted unidirectional from one N_Port to

another. Sequence initiator — The N_Port that begins a new sequence and transmits frames to

another N_Port. Sequence recipient — The N_Port that receives a particular sequence of data frames. Start of frame (SOF) delimiter — The ordered set that is always the first transmission

word of a frame. It is used to indicate that a frame will immediately follow and indicates which class of service the frame will use.

Special character — A special 10-bit transmission character, which does not have a corresponding 8-bit value, but is still considered valid. The special character is used to indicate that a particular transmission word is an ordered set.

Switch — A device that connects the fabric using a virtual circuit or a virtual packet circuit. The switch can make an electric connection between ports, or it can reroute packets through the switch.

Transmission character — A 10-bit character transmitted serially over the fiber. Transmission word — A string of four consecutive transmission characters. VI — Virtual Interface.

San topologies

SAN devices connected by Fibre Channel can be arranged using one of three topologies:

Point-to-point — A dedicated and direct connection exists between two SAN devices. Arbitrated loop — The SAN devices are connected in the form of a ring. Switched fabric — SAN devices are connected using a fabric switch. The fabric switch

enables a SAN device to connect and communicate with multiple SAN devices simultaneously.

Point-to-point

In the point-to-point topology, there is a direct connection between the devices. The bandwidth of that connection is dedicated entirely to that transaction. As a result, transactions are fast and relatively error free. However, a SAN based exclusively on this topology is expensive for large enterprises.

Communication bottleneckBefore a source device can communicate with a target device, the source device must log on to the network port of the target device by using a logon name and a password. The logon name and the password are set for a network port during the installation of network services on the target device.

Disadvantages of point-to-point

Although a two-way communication path exists between two devices, only one path can be used at a time. Devices can either transmit or receive, but they cannot do both simultaneously.

SAN devices in a point-to-point network must be physically connected to communicate with each other.

FC-AL

The FC-AL topology is a serial interface that creates logical point-to-point connections between ports on the loop. Several Fibre Channel arrays and multiple servers could be on the FC-AL. A simplified FC-AL consists of a:

Server equipped with a Fibre Channel HBA. Fibre Channel storage hub. Fibre Channel storage array with a Fibre Channel array controller installed.

ArbitrationEach port on the arbitrated loop has its own identity and can arbitrate for control. After it has control and the targeted port responds, bidirectional communication occurs.

Only one pair of ports on the loop can communicate at a time as a point-to-point connection, while the other ports on the loop act as repeaters.

The hub provides bypass switching at each port. This feature ensures continuity of the loop if any connected port should fail. When a device on the arbitrated loop fails, it is bypassed.

Switched fabric

A Fibre Channel switch transmits each packet only to the port connected to the destination device.

High performanceThe FC-SW topology provides higher bandwidth because each packet is routed to its destination port. This eliminates unnecessary traffic on the other ports and reduces the need for retransmissions of data because of collisions.

Routing tablesThe Fibre Channel switch routes data packets to their destination port based on a routing table. The routing table associates each port with the device attached to that port. The table is built as each Fibre Channel device periodically transmits its identity to the switch.

ComponentsA simplified FC-SW contains a:

Server equipped with a Fibre Channel HBA. Fibre Channel storage switch. Fibre Channel storage array.

Fibre Channel port connection

Ports have different names depending on how they are used with each device in a SAN. The mode of operation determines how the port is named.

A Fibre Channel port connection is where the cables are plugged. The hardware used to connect cables to ports in a SAN is called a Gigabit Interface Converter (GBIC). Port and GBIC are interchangeable terms. The GBIC is the physical connector and the port is the logical name.

In many cases, a single bus adaptor on hosts and devices support all of the listed port connections.

In the following table the E_Port is not shown for the switch because it connects only to another E_Port on another switch. The switches automatically configure to the appropriate ports depending on what type of port on the host or device it is being connected to. The only exception is the QL port, which has to be manually configured.

Host Device Hub

Ports N NLpub NLpri N NLpub NLpri FC-AL

F switch Yes No No Yes No No No

FL switch No Yes No No Yes Yes Yes

QL switch No Yes Yes No Yes Yes Yes

FC-AL hub No Yes Yes No Yes Yes Yes

Note: NLpub and NLpri are loop ports for private and public loops, which are explained later in the course.

Fibre Channel addressing

Fibre Channel addressing is identified by:

AL_PA — A 24-bit address that identifies a port. Port address — A subset of the WWN used by Fibre Channel networks that assign

N_port and NL_port addresses. WWN — A unique 64-bit address assigned to each node. If a node has more than one

port, each port is assigned a WWN. SNS — A server located on the switch that is used to keep track of WWNs and the

associated 24-bit N_Port IDs. FLOGI — A protocol used between a node (server or storage) and the fabric to

establish identification and capability parameters for subsequent communication.

Fibre Channel basics: Learning check

1. How far apart can Fibre Channel devices be if optical fiber is used as the physical medium? Choose the correct answer.

1km

5km

10km

15km

For help, see What is Fibre Channel?

2. What Fibre Channel gigabit bandwidths are available? Choose the correct answer.

1Gb and 2Gb

2Gb and 3Gb

3Gb and 4Gb

4Gb and 5Gb

For help, see Fibre Channel features

3. Which Fibre Channel layer transfers frame formats, performs sequence and exchange management, controls the flow of data, and administers the topologies? Choose the

correct answer.

FC-1

FC-2

FC-3

FC-4

For help, see Fibre Channel layers

4. What is the maximum frame size? Choose the correct answer.

512 bytes

1024 bytes

2148 bytes

4296 bytes

For help, see Framing protocol

5. Which framing class of service does not require acknowledgements? Choose the correct

answer.

Class 1

Class 2

Class 3

Class 4

For help, see Framing classes of service

6. How many WWNs are assigned to each node? Choose the correct answer.

One

Two

Three

Four

For help, see Naming and addressing

7. Which Fibre Channel port is the Link_Control_Facility within the fabric (switch) that attaches to an N_Port? Choose the correct answer.

NL_Port

F_Port

FL_Port

G_Port

For help, see Fibre Channel ports

8. In which topology are the SAN devices connected in the form of a ring? Choose the

correct answer.

Point-to-point

Arbitrated loop

Switched fabric

For help, see Three basic topologies

9. Which Fibre Channel addressing mode determines network parameters? Choose the

correct answer.

FLOGI

Port address

WWN

AL_PA

For help, see Fibre Channel addressing

10. What are valid port names for switches used in an FC-AL topology? Choose the correct

answer.

F, FL, and N

FL and QL

FL, QL, and NLpub

For help, see Fibre Channel port connection

11. What are the components of a frame? Choose the correct answer.

SOF, header, payload, CRC, and EOF

SOF, header, SCS, CRC, and EOF

SOF, CLS, payload, CRC, and EOF

Fibre Channel Arbitrated Loop: Objectives


Define Fibre Channel Arbitrated Loop (FC-AL). Describe FC-AL characteristics. Define FC-AL addressing and how it affects the arbitrated loop. Describe the relationship between the loop ID and the arbitrated loop physical

address (AL_PA). Define FC-AL loop initialization and how it affects the arbitrated loop. Describe FC-AL operation. Define arbitrated loops and switches. List the advantages and disadvantages of FC-AL for storage.

What is FC-AL?

FC-AL is a serial interface that:

Creates logical or virtual point-to-point connections between device ports.

Uses a minimum number of transceivers.

Does not use centralized switching.

Has information flowing in one direction around the loop.

This topology enables a single connection between one pair of ports at any point in time.

After a session is started (two devices

communicating), the other devices connected to the loop must wait until the connection ends.

Devices in the arbitrated loop share access, but only the active link has the full bandwidth. Therefore, only one pair of nodes can be communicating on the loop at the same time.

Arbitrated loop process The transmitter port on one node connects to the receiver port on

another node. This process continues until the last transmitter port connects back

to the first receiver port, which closes the loop. When nodes are added, they perform a loop initialization process

where the physical addresses of the arbitrated loop are assigned.

Features

Many devices can be on a loop, but only two communicate at a time. A loop can have as many as 126 ports. Each port discovers if it is on a loop during initialization. Every device participates in the loop initialization and receives a unique address. There

is no single permanent loop master.

Repeater function

As the data is sent in one direction around the loop, from the transmitting port of a node to the receiver port of another node, each port on the loop functions as a repeater.

The receiver port receives the data, which is changed back to a digital signal. The signal is regenerated, changed back to an optical signal, and retransmitted. The repeater does not buffer any of the information and, therefore, each node on the loop must operate at the same transmission rate

Loop Port State Machine

The Loop Port State Machine (LPSM) is responsible for performing the loop protocols. The loop protocols include the loop initialization, arbitration, and the opening and closing of loop communication circuits.

The LPSM receives controlling inputs from the hardware and firmware of the loop port and from the ordered sets received from the loop interface. These inputs cause the LPSM to progress through the states as the loop protocols are performed.

LPSM states

The LPSM consists of 11 states:

1. Initializing state — When a port is powered up, it enters the initializing state and starts the loop initialization process.

2. Old-port state — If no operational loop is detected, the port goes into the old-port state. In this state, the port functions like an N_Port until the LPSM detects an operational loop.

3. Open-init state — When an operational loop is detected, the port goes into an open-init state, where the rest of the loop initialization process occurs.

4. Monitoring state — When the initialization process is finished, the port goes into the monitoring state. In this state, the port acts as a repeater.

5. Arbitrating state — When a port needs access to the loop, it enters the arbitrating state and starts arbitrating for control of the loop.

6. Arbitration won state — When the port wins arbitration, it goes into the arbitration-won state (ARB_Won State).

7. Open state — The port sends an open command to the destination port and enters the open state. When a port is in the open state, it is called the open originator, and the FC-2 level is logically connected to the loop.

8. Opened state — When the destination port receives the open command, it enters the opened state, completing the loop circuit. When a port is in the opened state, it is called the open recipient, and the FC-2 level is logically connected to the loop so frame transmission can start.

9. Transmitted close state — Either port can send a close command (CLS) when frame transmission is completed. After a port sends a CLS, it enters the transmitted-close state (XMTD_CLS state) and then returns to the monitoring state.

10. Received-close state — After the other port receives the CLS, it enters the received-close state (RCVD_CLS state) and then returns to the monitoring state.

11. Transfer state — The last state a port can be in is the transfer state. A port can enter this state only if it is in the open state (the open originator). The open originator can enter the transfer state when sending a transmit close to the destination port. After the destination port closes the loop, the open originator

can leave the transfer port and re-enter the open state to send frames to a different destination port.

Port-bypass circuit

In a single-loop configuration, a failure of the loop or any device can be disastrous. It is not acceptable for the entire system to fail when a single device fails, is powered off, or is removed for service. To bypass the problem and enable the rest of the loop to continue operating as needed, a port-bypass circuit is used.

Most configurations of this type use an electrical port-bypass circuit. If a device fails, the port-bypass circuit automatically bypasses the failed device and enables the rest of the loop to continue operation.

Although an arbitrated loop with the port-bypass circuit is a significant improvement, it still does not completely ensure operation of the loop. A port and its bypass circuit could fail, causing the entire loop to fail.

Arbitrated Loop physical address

The AL_PA is a 24-bit address that identifies a port. In a loop topology, the eight least significant bits are used to identify a specific port.

If the arbitrated loop is connected to a fabric, the address is divided into two sections:

The first section, bits 0 through 7, represents a specific port. The second section, bits 8 through 23, identifies a specific loop.

Every frame carries a 24-bit source address and a 24-bit destination address in the frame header.

Port assignment sequence:

1. AL_PA is assigned during the loop initialization 2. Loop master generates and transmits 3. AL_PA bit map has returned to the loop master 4. Ports with no AL_PA value enter the nonparticipating mode

Relationship between loop id and AL_PA

The loop ID is the 8-bit loop address and the AL_PA is the 10-bit form of the encoded address. The loop ID is numbered in ascending priority and AL_PA in descending priority.

A higher loop ID number equals a higher priority. A higher AL_PA number equals a lower priority.

Only 126 NL_Ports are enabled on an arbitrated loop.

DisparityThe 8-bit and 10-bit encoded bytes have a property known as disparity. The loop ID and the AL_PA disparity properties can be positive, negative, or neutral. An 8-bit and 10-bit byte has negative disparity if there are more binary ones in the byte than binary zeroes. Conversely, the byte has positive disparity if there are more binary zeroes than ones.

Neutral disparity is when the number of binary ones equals the number of binary zeroes. This is required to eliminate clocking errors between sender and receiver.

Loop initialization

A loop performing a normal loop activity might fail when adding a device to the loop or changing the NL_Ports of loop devices.

Proper selection of loop devices, such as hubs, storage subsystems, and host bus adapters (HBAs), ensures that a loop resumes its normal activity whenever new devices are introduced into the loop.

An understanding of the loop initialization process helps to repair loop failures that might occur when adding a device to the loop:

The hub is switched on and

all currently active devicesthat are connected to thehub require an AL_PA to beassigned to them.

A new device is added to theloop and requires an AL_PAto be assigned to it.

The NL_Port of a device ischanged.

A loop recovers from a failure.

Loop initialization primitives

The loop initialization process is triggered when a loop device circulates an ordered set at least 12 times onto the loop. An ordered set is controlling data that the Fibre Channel protocol uses to communicate with a receiving device. Ordered sets include the start and end of frame bytes.

Open initializationWhen loop devices receive one of the ordered sets, they enter the Open_Init state. The device suspends all current operations and prepares itself for the loop initialization process.A loop device circulates one of the ordered sets within a loop. These ordered sets are also referred to as loop initialization primitives (LIPs).

A LIP is used to:

Initiate a procedure that results in a unique addressing for all nodes. Indicate a loop failure.

Reset a specific node.

A LIP is generated when a device is unplugged from a hub or plugged into a hub, powered off, or powered on.

These features describe the notebook without the optional Port Replicator.

Ordered set Event

LIP (F7, F7) Is circulated by a loop device that is switched on. The first occurrence of F7 indicates that the device is able to recognize itself within the loop. The second occurrence indicates that the device is yet to be assigned an AL_PA. The device circulates this ordered set because it would have lost its AL_PA when it was previously switched off.

LIP (F7,AL_PS) Is circulated when a loop device is moved from one hub port to another. F7 indicates that the loop device is able to recognize itself within the loop. AL_PS specifies the loop address that was previously assigned to the device. The device circulates this ordered set to indicate that a topology change has occurred within the loop.

LIP (F8, F7) Is circulated when the receiver of an HBA to which a loop device is connected fails. F8 indicates a loop-down state, and F7 indicates that the device must be assigned an AL_PA. The device circulates this message when it is switched on.

LIP (F8, AL_PS) Is circulated when the receiver of an HBA to which a loop device is connected fails. F8 indicates a loop-down state, and AL_PS specifies the loop address that was previously assigned to the device. The device circulates this message if it was active when the failure occurred.

Loop master selection

When all devices within the loop reach the Open_Init state, one of the devices needs to be assigned as the temporary loop master. The temporary loop master is responsible for carrying out the rest of the loop initialization process.

Loop initialization select masterA loop initialization select master (LISM) procedure is used to determine the device that acts as the temporary loop master:

1. Each loop device circulates an LISM frame that contains the port address and the worldwide names (WWN) of the device.

2. The neighboring loop device picks up the LISM frame from the loop and compares the WWN of the LISM frame with its own WWN. The neighboring device also checks whether the port address on the LISM frame is a valid FL_Port.

3. If the port address on the LISM is greater than its port address, the neighboring device puts the LISM frame back into the loop.

4. If the port address on the LISM is less than its own port address, the neighboring device replaces the port address on the LISM frame with its own port address and puts back the modified LISM frame into the loop.

This sequence is repeated until all devices circulate the same LISM frame within the loop. Therefore, a loop device gets back its own LISM frame, indicating that it has the maximum priority within the loop. This loop device then acts as the temporary loop master. The loop master circulates a special ordered set, ARB (F0), to notify the other devices about the completion of the LISM procedure.

AL_PA assignment

The purpose of the loop initialization process is to assign an AL_PA to each of the loop devices. The temporary loop master circulates a set of four frames that are used to assign unique AL_PAs to each of the loop devices.

Each frame consists of:

An address map of all possible 4-bit AL_PAs that can be assigned to the devices within the loop.

A header that defines which of the loop devices are accepted to select an AL_PA from the frame.

A status bit for each AL_PA that specifies whether or not an address has been assigned to any of the loop devices.

AL_PA loop device assignment1. The loop master circulates a loop initialization fabric address (LIFA) frame. This frame

enables all public loop devices that were assigned an AL_PA during the previous loop initialization process to select an AL_PA from the list. The public loop devices select the AL_PA that was previously assigned to them from the LIFA frame.

2. After the loop master receives the LIFA frame back, it circulates a loop initialization previous address (LIPA) frame. This frame enables all private loop devices to select the AL_PA that was previously assigned to them from the address map.

3. After the loop master receives the LIPA frame back, it circulates the loop initialization hard address (LIHA) frame. This frame enables all NL_Ports that have a dual in-line package (DIP) switch or a jumpered address to select an AL_PA from the address map.

4. After the loop master receives the LIHA frame back, it circulates the loop initialization soft address (LISA) frame. This frame enables all loop devices that are yet to be assigned an AL_PA to select an AL_PA from the address map.

Position mapping

According to Fibre Channel standards, the loop initialization process terminates after the AL_PA assignment is complete. Vendors who support Fibre Channel have incorporated an additional positional mapping subroutine in their products. The position mapping subroutine is used to determine how devices are organized within the loop topology. Positional mapping is used for diagnostic purposes and fine-tuning loop configuration.

Positional mapping involves the following steps:

1. The temporary loop master circulates a loop initialization report position (LIRP) frame within the loop.

2. Each loop device picks up the LIRP frame, appends its own AL_PA to the frame, and puts the LIRP frame back onto the loop.

3. After the temporary loop master receives the LIRP frame back, it recirculates the frame within the loop.

4. Each loop device copies the LIRP frame. 5. The loop initialization process terminates after the positional mapping

process is complete. 6. The loop master indicates the completion of the loop initialization process

by circulating the CLS and IDLE frames (loop is closed, no activity) within the loop.

7. When each loop device receives the CLS frame, it moves out of the open-init state and resumes normal activity.

8. The IDLE frames are circulated within the loop until a new communication process is triggered.

FC-AL operation

A loop device must gain access to the loop before it cancommunicate with another loop device. Arbitration is the processby which a loop device determines if the loop path is free for it tocommunicate and gain control of the loop.

A loop device can access the loop path according to the followingfactors:

Priority of the AL_PA loop devices Status of an access variable that is stored in the LPSM

of a loop device

x-AL_PA of the arbitrating deviceA loop device wins an arbitration process if it receives back theARB(x) ordered set that it transmitted. Additionally, if two or moredevices arbitrate simultaneously, an arbitrating loop device thathas the greatest priority wins the arbitration.

Note: An IDLE frame is transmitted over the loop path if the looppath is not being used by any other device and is free fordata transmission.

Loop arbitration

Gaining access to the loop pathA loop device performs the following sequence of steps to gain access to the loop path:

1. The loop device checks to see if the loop path is busy. 2. If the loop path is not busy, the device transmits an ARB(x) ordered set that contains its

own AL_PA. The device transmits an ARB(x) ordered set even if another device currently owns the loop path. However, if frames are currently traversing the loop path, ARB(x) is issued only between two successive frame transmissions.

3. ARB(x) circles the loop and reaches the loop device that arbitrated, indicating that the loop path is free for data transmission. Then, the arbitrating loop device reaches the ARB_Won state and a subsequent OPEN state, and is ready for data transmission.

Simultaneous arbitrationHow lowest priority gains access

Simultaneous arbitration

If two or more devices arbitrate simultaneously, each of the arbitrating devices receive the ARB(x) ordered set that was sent by its neighboring arbitrating device. The arbitrating devices then compare the AL_PA on the received ARB(x) with their own AL_PA.

If the priority of the AL_PA on the received ARB(x) is greater, it puts the ordered set back onto the loop. If the AL_PA on the received ARB(x) has a lower priority, the neighboring arbitrating device replaces the AL_PA with its own AL_PA and puts the modified ARB(x)

ordered set back onto the loop.

Press

How lowest priority gains access

Because high-priority devices win the arbitration process, low-priority devices are kept from gaining loop access. Loop access variables are used to ensure that low-priority devices also gain access to the loop path.

How lowest priority gains access:When a loop device wins an arbitration process, the loop access variable on its LPSM is set to zero. The device cannot arbitrate again as long as its access variable is zero.

To win a subsequent arbitration, a loop device performs these steps:

1. After a loop device wins an arbitration for the first time and completes data transmission, it transmits an ARB(F0) ordered set onto the loop. ARB(F0) has the lowest priority.

2. If no other device is currently arbitrating, the loop device receives back the ARB(F0) that it transmitted. This indicates that the loop path is free and no other device requires access to the loop path. Then, the state of the loop access variable on the loop device, which is currently competing for a subsequent arbitration, is set to one.

3. If another device starts arbitrating, it picks up the ARB(F0) ordered set from the loop, attaches its own AL_PA, and puts the modified ARB(x) onto the loop. As a result, the loop device, which is currently competing for a subsequent arbitration, does not receive the ARB(F0) that it transmitted.

Arbitrated loop and switches

FC-AL switchFC-AL can also be supported in a switch environment. The FC-AL switch provides increased performance and stability compared to the Fibre Channel hub technology.

Based on a nonblocking switched backplane, the FC-AL switch offers enough switch 6yytyii

Public loop

If an active FL_Port is on the loop, it is considered a public loop; an arbitrated loop that is connected to a fabric. The public loop can accommodate up to 126 NL_Ports and one FL_Port.

The FL_Port extends the number of nodes for communication. Using this port, a private loop can be connected to the public loop. This extended configuration uses Switched Fabric topology.

Private loop

If no active FL_Port exists on the arbitrated loop, it is called a private loop; an arbitrated loop that stands on its own. It is not connected to a fabric. The private loop can accommodate up to 126 NL_Ports.

The preceding figure shows two private arbitrated loops. Nodes on loop 1 cannot communicate with nodes on loop 2.

Private loop considerations:

Devices beyond 126 NL_Ports do not receive an AL_PA, but act as repeaters on the loop.

A private loop does not contain an FL_Port.

Advantages and disadvantages of FC-AL for storage

Advantages

FC-AL for storage is a low-cost solution for connecting peripherals and hosts. It supports up to 126 NL_Ports per loop with practical implementations not greater than

60. The FC-AL hub and switch port bypass circuits enable hot-plug device repair.

DisadvantagesBecause the number of nodes that make up the loop is very high, communication can be very slow. The Fibre Channel loop topology works well, provided the number of nodes connected to the loop is not very high. It is recommended that not more than 20 nodes be connected in a Fibre Channel loop.

Fibre Channel Switched Fabric might be a better solution because of the disadvantage of potential slow communication and no great advantages.

Fibre Channel arbitrated loop: Learning check

1. The receiver port receives the data, which is changed back to a digital signal and the signal is regenerated, changed back to an optical signal, and retransmitted. What FC-AL characteristic does this describe? Choose the correct answer.

Repeater function

LPSM

AL_PA

Bypass circuit

For help, see FC-AL characteristics

2. What is the size of the AL_PA address that identifies a port? Choose the correct answer.

8-bit

16-bit

24-bit

32-bit

For help, see Arbitrated loop physical address

3. Select the correct statement regarding loop ID numbers and AL_PA numbers. Choose

the correct answer.

A higher loop ID number equals a higher priority and a higher AL_PA number equals a lower priority.

A higher loop ID number equals a higher priority and a lower AL_PA number equals a higher priority.

A higher loop ID number equals a higher priority and a lower AL_PA number equals a lower priority.

A higher loop ID number equals a lower priority and a higher AL_PA number equals a higher priority.

For help, see Relationship between loop ID and AL_PA

4. What process must be executed when a new device is added to a loop requiring an AL_PA to be assigned to it? Choose the correct answer.


AL_PA assignment

Position mapping

Loop initialization

For help, see Loop initialization

5. What loop initialization primitive ordered set is circulated when the receiver of an HBA, to which a loop device is connected, fails? Choose the correct answer.

LIP (F7, F7)

LIP (F7,AL_PS)

LIP (F8, F7)

LIP (F8, AL_PS)

For help, see Loop initialization primitives

6. Select the correct statement regarding the sequence of steps to determine a temporary loop master. Choose the correct answer.

Each loop device circulates a WWN that contains the port address and the LISM frame of the device.

The neighboring loop device picks up the LISM frame from the loop and compares the WWN of the LISM frame with its own.

If the port address on the LISM is less than its port address, the neighboring device puts the LISM frame back into the loop.

If the port address on the LISM is more than its own port address, the neighboring device replaces the port address on the LISM frame with its own port address and puts back the modified LISM frame into the loop.

For help, see Loop master selection

7. How many frames does the temporary loop master circulate that are used to assign unique AL_PAs to each of the loop devices? Choose the correct answer.

One

Two

Three

Four

For help, see AL_PA assignment

8. What is the subroutine that is used to determine how devices are organized within the loop topology? Choose the correct answer.

Loop initialization

Position mapping


AL_PA assignment

For help, see Position mapping

9. What is the loop access variable set to when a loop device wins an arbitration process? Choose the correct answer.

Zero

One

On

Off

For help, see Loop arbitration

10. What is a public loop? Choose the correct answer.

A loop that is inaccessible to other nodes that are not a part of the loop

A loop that is not a part of the SAN fabric

A loop that is not connected to any other loop

A loop with an active FL_Port

For help, see Public loop

11. How many NL_Ports can a private loop accommodate? Choose the correct answer.

Up to 32

Up to 64

Up to 126

Up to 252

For help, see Private loop

Fibre Channel switched fabrics: Objectives


Describe the switch and fabric topology features and characteristics. Identify inter-switch link (ISL) operations. List the steps for Fibre Channel initialization, including fabric login and and simple name

servers. Describe cascading switches. Determine the difference between load sharing and load balancing. List zoning characteristics and features.

Switched fabric topology

A switched fabric is a flexible architecture that uses a group of switches connected through inter-switch links (ISLs) to provide access to all devices on the SAN. Each device has full bandwidth capability between itself and the switch.

In this diagram, the switches are connected to provide access to other devices on the SAN.

Fabric switches

A SAN fabric can include a single switched fabric or hundreds of switched fabrics.

Fabric switches:

Connect up to 16 million nodes. Act like routers with ports (only those ports communicating see the traffic). Provide high bandwidth (multiple paths are enabled concurrently). Provide electrical and logical isolation. Are more expensive than hub configurations.

Any-to-any connectionPorts on one node can communicate with ports on other nodes connected to the same fabric. With the fabric topology, many connections can be active at the same time.

The any-to-any connection service and peer-to-peer communication service provided by a fabric is fundamental to Fibre Channel architecture. Fibre Channel switches can communicate simultaneously through the Fibre Channel Switched Fabric (FC-SW) protocol.

Fabric features

A switched fabric has features that help speed up communication within a fabric network.

Frame algorithms Fabric switches use either cut-through or store-and-forward algorithms to direct data from a source device to a target device.

The cut-through algorithm is used in fabric switches to speed up data routing. When a frame enters the fabric switch, the cut-through algorithm looks at the destination identifier (D_ID) of the frame and routes the frame to the proper port. Because the D_ID is in the frame header, the routing happens as soon as the frame enters the switch.

The store-and-forward method reads the entire frame into a buffer before determining the exit port.

BufferingIf a switch receives requests for data transmission from many devices simultaneously, regardless of the routing algorithm used, the switch might not be able to route all the data simultaneously. The routing algorithms discard the frames that they cannot process.

In such cases, frames are buffered on the F_Port of the switch to which the transmitting and receiving devices are connected. This enhances the performance of the switch.

Fibre Channel addressing The N_Ports are assigned a unique 24-bit address:

The first most significant bit (MSB) submits to the domain address, which is the address of the fabric switch to which the device is connected.

The second MSB submits to the FL-Port (fabric loop) address. The third MSB refers to the F-Port address, which is the address of the port to which

the device is connected.

Fabric element

In the fabric topology, at least one active element (switch, ring, or hub) must be placed between ports. This element is responsible for responding to fabric login requests, managing class of service for the fabric, and assigning addresses.

A fabric element can:

Attach N_Ports. Attach arbitrated loops. Serve as the root element for distributed fabric elements.

A fabric element is the smallest entity that can function as a complete fabric topology. It must have at least three F_Ports or FL_Ports to make routing decisions. When multiple fabric elements are interconnected, they form a cooperative unit that is still a fabric.

Fabric and loop comparison

Description Fabric Loop

Ports NL and FL_Ports N and L_Ports

Access FLOGI Arbitration

Communication One-to-one connections made between network nodes and switch ports

Shared media

Bandwidth High speed because of switches that can aggregate integrated circuitry and provide cut-through switching

Low speed because of loops configured with hubs and switches that do not support cut-through technology

Network services

Supports services for coordinating network activities

Requires connection to a fabric for access to the network activity services

Segmentation or zoning

Yes None

Connections 224 nodes 126 NL_Ports

Inter-switch link

The connection between switches is called an Inter-switch link (ISL). When switches are connected by an ISL, they share data and information using the FC-SW protocol, which provides the any-to-any device communications.

Multiple physical ISL connections can exist between each port on the switch.

ISL characteristics

Each connection involves two ports operating in E_port mode. The current limit of active ISLs between two switches is eight. Multiple ISLs between switches increase bandwidth when required by the environment. Each ISL constitutes a hop. Hops are used during the design process to ensure that the fabric complies with design

rules.

ISL terms and operations

Domain ID The domain ID identifies a switch in a fabric. The SAN switch configuration can have up to 239 switches in a fabric. Cascading the Fibre Channel switches and SAN switches requires compatibility mode addressing that reduces the number of addressable ports to 32.

Hops Hops are data routing through the fabric, where a single hop is one or more ISLs between any

two switches. For efficiency, minimize the number of hops between devices that communicate in a SAN. The maximum number of hops in a fabric based on SAN switches is seven.

Path A path is a chain of switches from the source to destination that enables two devices to communicate. Fabric topology software provides information on the fabric, including all existing paths, their associated hop count, and cost metric.

Fabric shortest path first (FSPF) This dynamic path selection protocol provides for short convergence times when failures occur, and routing loop-free paths at all times. It computes the best path between any two switches in the fabric, and then programs the hardware routing tables. The protocol starts running automatically at restart time.

Selected route A selected route is a map between an input port and an output E_port to reach the next hop. The switch dynamically establishes routes based on the optimum paths. SAN switches enable user-defined static routes that can be defined for dedicated bandwidth.

Path determination

A Fibre Channel switch compares a path based on a cost metric. The cost of a given path is the sum of the costs of all the traversed ISLs.

The optimum path has the lowest associated cost. More than one path can be selected if multiple paths with equal costs exist. ISLs with a higher speed (such as greater than 100MB/s) have lower costs.

Example: The cost metric of 200MB/s paths is 500.

This diagram displays two paths from the server to the storage system:

Path 1 goes directly from domain 1 (port 15) to domain 3 (port 7). Path 2 goes from domain 1 (port 12) to domain 2 (port 3); then from domain 2 (port 13)

to domain 3 (port 0).

Although both path 1 and path 2 are valid, path 1 has a cost metric of 1000 compared to 2000 for path 2. The switch selects path 1.

FSPF features

FSPF features include:

Fast computation of new paths in case of failure

Routing loop-free topologies at all times Traffic load sharing over equivalent cost metric paths High-priority FSPF frames Completely flexible topology Guaranteed in-order delivery during topology changes Negligible bandwidth use by the FSPF frames Same technology for unicast, broadcast, and multicast path selection

FSPF frames have the highest priority in a fabric. This guarantees that a control frame is not delayed by user data on a congested link.

The FSPF protocol makes minimal use of the bandwidth of the ISLs. In a stable fabric, without topology changes, a switch transmits about 64 bytes every 10 seconds on each ISL in both directions.

Fibre Channel initialization

Fabric switches offer the following services to detect and respond to topology changes:

Fabric login (FLOGI) service Simple name server (SNS) service State change notification service (SCNS

Logging into fabric (FLOGI)

In the fabric environment, the N_Port must go through a login procedure to establish the parameters of its operating environment.

This diagram displays the steps for the login process. The first step is the fabric login (FLOGI), followed by a port login (PLOGI) to establish communication with another N_Port.

Switch fabric addressingAddress limitationsFibre Channel port typesFibre Channel port table

Switch fabric addressing

Both fabric and N_Port logins to the fabric use similar procedures. They are distinguished by different destination (D_ID) and source (S_ID) identifiers. Both use the extended link service (ELS) commands to establish the login.

Before data can be exchanged between ports, the N_Port must know:

What the interconnect topology is (point-to-point, fabric, or arbitrated loop). If there are other N_Ports in the environment. What classes of service are supported by the fabric. What service parameters are applicable. What error recovery procedures can be used.

Address limitations

The size of a fabric switch environment is practically unlimited. Only the number of N_Ports that can be identified in the frame header limits the number of ports that can attach to nodes in a fabric topology.

Given that the field carrying this information (the destination address identifier field) contains 24 bits, the limit is just over

16 million addresses. Consider these points:

Only the number of present fabrics limit the total number of ports in a system. A system can include more than one fabric, and a node can have each N_Port or

NL_Port attached to a different independent fabric. Each fabric is a closed address space with addresses that might duplicate those in

other fabrics. N_Ports or NL_Ports in one fabric cannot communicate directly with those in another

fabric because there is no path to them.

Ports can communicate through the Internet if bridges and routers are connected at the edges of the fabrics.

Fibre Channel port types

Fibre Channel port tablePort Type Usage

N_Port Node Point-to-point or fabric

NL_Port Node Node connected to an arbitrated loop

F_Port Fabric Fabric port

FL_Port Fabric Fabric connected to an arbitrated loop

L_Port Loop Hub port on an arbitrated loop

L_C_F (Link Control Facility)

Loop A hardware facility that attaches to each end of the link and manages data transmission and reception. It is located within each port, contains a transmitter and receiver, and provides the logical interface to the node.

Rx (Receiver) The portion of the link control facility dedicated to receiving an encoded bit stream from the media, converting it into transmission characters decoded by using the rules specified by FC-PH

Tx (Transmitter) The portion of the link control facility dedicated to converting valid data bytes and special codes into transmission characters using transmission code rules. The Tx then converts these characters into a bit stream and transmits it into an optical or electrical transmission media.

G_Port A generic switch port that operates in either E_Port mode or F_Port mode

E_Port An inter-switch expansion port used to connect to an E_Port of

another switch to build a larger fabric 5 of 5

Simple name server service

The simple name server (SNS) service provides information about devices connected to any switch in the fabric. An SNS resides on each fabric switch. This function enables external devices to discover other fabric-connected devices.

The SNS service manages and registers objects in a database that relates various external device entities to each other, including:

Mappings between N and NL_port 24-bit Fibre Channel physical addresses World Wide Names (WWNs) IP addresses Fibre Channel Class-4 device types Initial processes associators

External devices can register and query this information using the SNS function with the commands nsShow and nsAllShow.

The nsShow command displays the local name server information, which includes information about devices connected to the local switch and cached information about devices connected to other switches in the fabric.

The nsAllShow command displays the port IDs of all devices in all switches in the fabric.

State Change Notification

The process of state change notification occurs when devices need to notify other devices of a change in state. The two methods used to accomplish this in a switched environment are:

State Change Notification (SCN) — This is the process of one switch notifying another switch of the state of a change in the topology. SCN enables one N_Port to notify another N_Port of a change in port state. For instance, a server might be notified if a disk drive goes offline.

Registered State Change Notification (RSCN) — Unfortunately not all N_Ports receive SCN notification. To handle this situation, N_Ports register a request to be notified of a topology change. This is achieved using RSCN.

Cascading switches

Cascading is an interconnection of Fibre Channel switches. A single switch fabric can include a limited number of interconnected switches. Two options to increase connectivity are:

Increase the port count per switch. Connect multiple switches to build a cascaded fabric.

Building a bigger switch might seem attractive, but it can be cost prohibitive, especially when preserving the nonblocking characteristic of the switch. Bigger switches can be justified only for mission-critical applications.

Cascading:

Is a reliable, scalable, and cost-effective alternative to building larger fabrics. Enables fault-tolerant configurations that provide continued operation in the event of

system failures. Supports switches that can be serviced without interruption. Enables hops between different models of Fibre Channel switches, providing that

configuration parameters are the same or compatible.

Cascading routes

Using the FSPF protocol, the switches establish optimum routes between the domains based on the cost metric of the existing paths. These routes are then programmed into the routing tables of the switches.

The optimum route from domain 1 to domain two is in port-3 out of port-11, one hop (1000 units).

The optimum route from domain 1 to domain 3 is in port-3 out of port-5, one hop (1000 units). A third path from domain 1 to domain 3 is available at a cost metric of two hops (2000 units). If the ISL between domain 1, port-11 and domain 2, port-1 were to fail, the switch would dynamically reconfigure the route to use the path from domain 1, port-5 to domain 3, port-3 and domain 3, port-2 to domain 2, port-5.

Load balancing sharing

In a SAN, servers and storage can have bottlenecks caused by data being used by one resource and not enabling the other resources to access it.

Two methods are used to resolve these bottlenecks and performance concerns: load balancing and load sharing.

Load balancingLoad sharing

Load balancing

Load balancing enables a storage or server system to provide requested data when one storage or server system is busy and cannot handle the request. Therefore, load balancing is provided between resources. More than one HBA in the server is used to balance the I/O load to storage disks.

Load sharing

Load sharing enables resources to share data across the servers and storage by dynamically rerouting or providing multiple paths. In this diagram:

Eight servers attached to Domain 1 must communicate with eight storage systems attached to Domain 2.

When multiple paths of equal cost are available, the switch allocates routes between source and destination in a round-robin fashion to share the load across the available paths.

If an ISL fails, the switch dynamically reconfigures the routes to use the remaining ISLs.

If two devices are using one ISL and another ISL comes online, the switch will reroute one of the devices to the new ISL.

Load sharing is conducted on a device basis, not a Fibre Channel frame basis.

Zoning features

Zoning divides the fabric into virtually smaller fabrics. A host or device can communicate only with other servers or devices within the same zone used to set barriers between operating environments.

Zoning has the potential to separate operating systems on the same fabric to secure storage devices against unauthorized servers. Zone members "see" only members in their zones, and access only one another.

Features

All devices connected to a fabric can be configured into one or more zones. Devices in the same zone see each other; devices in different zones cannot.

Zoning is a licensed feature that comes standard with most fabric switches.

Zoning types

Port-based zoning Address-based zoning

Port-based zoning

Port-based zoning, also known as hardware zoning or hard zoning, is enforced entirely by hardware. It physically blocks access to the zone from outside the zone.

Two databases used by port-based zoning are:

Zone configuration — The zone configuration database is replicated to all switches in the fabric using vendor-unique ISL commands.

N_Port login — The N_Port login data is stored locally on each switch and is used to map the WWN in zone definitions to a physical port number.

Address-based zoning

Address-based zoning, also known as software zoning, is based on the SNS and is enforced throughout the fabric. This form of zoning is the most flexible because it relates to the World Wide ID (WWID) and is independent of the port that the zone member is connected to.

Address-based zoning on the SNS service does not impact switch performance because there is no change to the SNS access protocol.

Fibre Channel switched fabrics: Learning check

1. A switched fabric can connect up to how many nodes? Choose the correct answer.

126

227

8 million

16 million

For help, see Switched fabric topology

2. Which port supports fabric switch direct connection? Choose the correct answer.

F_Port

L_Port

N_Port

NL_Port

For help, see Switched fabric topology — Features

3. What is an inter-switch link (ISL)? Choose the correct answer.

The connection between one or more switches

The connection between two or more switches

The connection between two or more servers

The connection between two or more storage systems

For help, see Inter-Switch link

4. How many switches can be supported by a SAN switch configuration in a fabric? Choose

the correct answer.

220

239

269

284

For help, see Inter-Switch link — SAN switches

5. Which statement correctly describes fabric login (FLOGI)? Choose the correct answer.

This is performed on every N_Port in the environment with which the N_Port communicates.

This determines network parameters and is done once or twice depending on whether the fabric can assign port identifiers.

This is performed on every L_Port in the environment with which the NL_Port communicates.

For help, see Logging into fabric (FLOGI)

6. Which port address is used for a Fibre Channel switch? Choose the correct answer.

8-bit port address

12-bit port address

16-bit port address

24-bit port address

For help, see Switched fabric topology

7. Which of the following lists the two options to increase switch fabric connectivity? Choose the correct answer.

Increase the number of storage units per switch and connect multiple routers to build a cascaded fabric.

Increase the port count per switch and connect multiple switches to build a cascaded fabric.

Increase the number of servers per switch and add storage to build a cascaded fabric.

For help, see Cascading switches

8. Load sharing enables resources to share data across the servers and storage by dynamically rerouting or providing multiple paths. Choose the correct answer.

True

False

For help, see Load sharing vs load balancing

9. Devices in the same zone cannot see each other; devices in different zones can. Choose

the correct answer.

True

False

For help, see Zoning

10. Which is a method used to separate devices into virtual segments for performance or security purposes? Choose the correct answer.

Port zoning

State change notification

Registered state change notification

For help, see Zoning

Fibre Channel cabling: Objectives


Describe the two types of Fibre Channel cabling used in a SAN implementation: Copper cabling Coaxial Twinaxial Shielded Twisted Pair (STP) Unshielded Twisted Pair (UTP)

Fiber optic cabling Structure and composition of a fiber optic cable Types of fibre optic cable Connectivity Grades of fibre optic cable Dispersion Graded index MMF cable Fibre Channel cabling considerations

Identify the various connectors used in a SAN implementation. GBIC GLM MIA Connector for copper cabling

Compare copper to fibre optic cabling. Identify distance, cabling types, and transceivers for 1Gb/2Gb Fibre Channel

Cabling

SAN cables are the physical links that connect all the different components of the SAN.

Fibre Channel cabling differs in the type of physical media used for data transmission. Fibre Channel works with both copper and optical cables. Regardless of the type of medium used, the performance for all Fibre Channel cabling is rated at 100MB/s and above.

However, fiber optic cables are the most commonly used type of cable in Fibre Channel SANs. The type of cable does not affect the speed of the network. Fibre Channel networks today operate at 1Gb/s or above.

CopperWhen Fibre Channel was first introduced to the market, the cables were made from copper, which limited the distance between SAN devices. Copper cables are rarely used in SANs today.

Fiber opticThe industry adapted fiber optic cables to increase the speed and distance that data could travel between SAN devices. The type of cable and the wavelength of light used determines the distance between devices.

Copper cables characteristics

Copper cabling is the time-tested method of interconnecting network nodes. With the increasing use of Gigabit Ethernet, the older copper-based cables have been upgraded to support transfer rates of about 1Gb/s.

Copper cabling can be used for data transmission to distances up to 30m (98.42 ft). It is best used for short distances such as within a building.

A Fibre Channel device to a copper cable is incompatible. This is where the copper gigabit interface converters (GBICs) and media interface adapters (MIAs) are used. These connectors act as the interface between the Fibre Channel-based SAN devices and copper-based cables.

Characteristics

Inexpensive No laser required (uses electrical pulses) Shorter distance than optical fiber Same throughput rates over supported distances as optical fiber

Limitations

Exposure to electromagnetic induction (EMI) and radio frequency interference (RFI), which can instantly reduce the quality of the signal

High rate of signal deterioration (attenuation) if the signal has to traverse long distances Affected by external noises Distance limitations, which is why copper cabling is recommended only for use inside a

cabinet or a rack. Low bandwidth compared to fiber optic cabling Possibility of short circuits, sparks, and spark-induced fires

Two types of GBICsTypes of copper cables

GBICs

There are two types of copper GBICs.

Intercabinet (active) The active GBIC uses additional circuitry to implement the signals used by hubs, switches, and devices to manage the operation and report status of the transmitter and receiver circuitry.

Intracabinet (passive) Devices connect through passive GBICs and are closer in proximity of each other to lower the maximum transmitter voltage requirements for the reduced length cables. GBICs contain no circuitry to amplify the transmitted signal or buffer the received signal. The transmitted signal is generated by the hub, switch, or device, and is passed through the GBIC to the receiver. The passive GBIC cannot report transmitter faults.

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Types of copper cables

The Fibre Channel standard defines four types of copper cables:

Coaxial Twinaxial Shielded Twisted Pair (STP) Unshielded Twisted Pair (UTP)

Coaxial This type of cable comprises two conductors that share a common axis and are separated by an insulating plastic foam.

TwinaxialA twinaxial cable contains two inner conducting copper wires instead of one. This is the most commonly used Fibre Channel copper cabling.

Shielded Twisted Pair (STP)This type of cable comprises bundled pairs of wire shielded by a foil. These moderately expensive cables can support data transfer rates within the range of 16 to 155Mb/s.

Unshielded Twisted Pair (UTP) A UTP cable lacks the shield that is present in an STP cable. As a result, the cable suffers from the effects of crosstalk. UTP cables use RJ-45 connectors.

Fibre Channel cable terms

To comprehend SAN characteristics, you need a general understanding of the different properties associated with Fibre Channel cabling. Common Fibre Channel cabling terms to be aware of when configuring the SAN are:

Attenuation Dispersion GBICs Macro bending Micro bending Refraction

Wavelength Cone of acceptance Numerical aperture

These terms are defined on the following pages.

Fiber optic cables characteristics

Unlike copper-based cables, fiber optic cables can provide long distance connectivity of 10km (32,808 ft). Fiber optic cables do not suffer from EMI, RFI, or magnetic fields. These cables are an optical data transmission that is based on the fundamental principle of total internal reflection.

Fiber optic cables have an extremely low rate of attenuation because light signals do not deteriorate over long distances. They provide high bandwidths and are absolutely immune to short circuits, sparks, and spark-induced fires.

Characteristics

Expensive compared to copper cabling High bandwidth because light pulses can travel faster Longer distances because optic light pulses can travel greater distances Not affected by external noises

Limitations

Fibre Channel supports various cable types. Connecting devices with various types of cables can lead to problems such as poor connections and damaged cables and connectors.

Precautions have to be taken to protect all optical components from heat, chemicals, contaminants, or any sort of axial or lateral movement to avoid a fiber optic cable from bending.

The type and diameter of a fiber optic cable limits the maximum distances between servers and storage devices in a SAN installation.

Laser fiber optic cables are more expensive than copper cables.

How fiber optic cables workStructure and compositionTypes of fiber optic cablesComparing SMF and MMF cablesComparing cable length limitationsConnectivityCable labelingGrading

How fiber optic cables work

Fiber optic cable is based on the principles of optics. For data to be transmitted as light pulses, electrical signals must be converted into light signals at one end of a fiber optic cable and back to electrical signals at the other end of the cable.

Fiber optic cables:

Transmit in the form of light pulses that travel down through the core. Hold and reflect the light beam through the core of the innermost layer. Reflect the light beam that travels down the core to the cladding.

Core and claddingThe core and the cladding differ in their refractive indices (RIs). The core has a higher RI than the cladding. This difference causes the total internal reflection of light and holds the light wave contained in the cable.

Pure laserThe performance of an optical network depends on the glass that makes up a fiber optic cable and the light that carries the information to be transmitted.

A laser is an example of a light source. It produces light that is monochromatic and is therefore referred to as pure. If a laser is pure, it can transmit data signals over longer distances and at higher bandwidths.

Structure and composition

A fiber optic cable is made of glass that is drawn into a very thin strand several miles long. The thickness of a fiber optic cable is comparable to that of a human hair.

A cross-section of a fiber optic cable reveals three layers, starting from the outside and proceeding inwards.

Jacket — The jacket is made of an acrylate coating. It protects the cladding and the core, and allows you to handle the cable without touching the inner fiber made of glass. The jacket also provides protection against abrasion, oil, solvents, and other contaminants.

Cladding — The cladding is made of pure silica. Core — The core is made of germania-doped silica.

Types of fiber optic cables

The two types of fiber optic cables are single-mode and multimode. The main distinction between single-mode fiber (SMF) and multimode fiber (MMF) is the physical diameter of the core.

Single-Mode fiber These cables provide a single path for the propagation of a light signal. They are used to connect devices that are located over longer distances, spanning up to 10km.

The single light-wave transmission eliminates any distortion that can result from overlapping light pulses.

SMF provides the least signal attenuation (weakening of signal) and the highest transmission speeds.

The core diameter of SMF cables are only obtained at high costs. Therefore, when choosing an SMF cable, high cost is one of the major deciding factors, along with increased bandwidth and longer distances.

Multimode fiber The diameter of multimode fiber is large enough to enable multiple streams of light to travel different paths from transmitter to receiver. Shortwave lasers are used with multimode fiber for transmitting over medium distances.

These cables provide multiple paths for the light signal to travel.

Comparing SMF and MMF cables

The small diameter of single-mode fiber enables one coherent stream of light to travel a single path. Longwave lasers are used with single-mode fiber to transmit data over long distances. Because it is typically used for carrying signals over long distances, single-mode fiber is ordered and cut to specified lengths. Single-mode fibers used in networking and data communications have a single-mode, step-index fiber.

The diameter of multimode fiber is large enough to enable multiple streams of light to travel different paths from transmitter to receiver. Shortwave lasers are used with multimode fiber for transmitting over medium distances.

Comparing cable length limitations

Two factors determine the limit of the transmission distance capability of a fiber optic cable:

Data transmission rate — With an increase in the data transmission rate, the transmission distance capability of each fiber optic cable type tends to decrease.

Attenuation — Connectors reduce the strength of a signal. The number of connectors used affects the transmission distance capability of a fiber optic cable.

Connectivity

Fiber optic cables connect to devices through small form factor (SFF) pluggable optic transceivers. Transceivers are attached to both the ends of the core of a fiber optic cable. They receive information in the form of electrical digital signals, convert them, and emit light pulses.

Note: A transceiver combines the functionality of a transmitter and a receiver into one package.

There are two types of SFF transceivers:

Shortwave (SW) laser — SW lasers provide connections for transferring data over short distances: 2m to 500m (7 ft to 1,640 ft). They transfer data through MMF cables.

Longwave (LW) laser — LW lasers provide connections for transferring data over long distances up to 20km (65,616 ft). They transfer data through SMF cables.

Cable labeling

The most commonly used fiber optic cable sizes are 50/125 fiber, 500m (1,640 ft) and 62.5/125 fiber, 175m (574 ft). The numbers on a label indicate that the diameter of the core Fibre Channel cable is 50µ and that of the cladding is 125µ. The size of the cable decides the usable length of the cable. Cables are also colored differently to distinguish one from the other.

Example: Cables with core diameters 9µ, 50µ, and 62.5µ are colored yellow, orange, and slate gray.

This table lists the Fibre Channel standard specifications for the types of fiber optic cables and transceivers that are best suited for a specified distance.

Data transmission distance

Type of fiber-optic cable Type of transceiver

< 300m (984 ft) SFM or MMF Any type can be used

300m to 500m (984 to 1,640 ft)

SFM LW laser

> 500m (1,640 ft) SFM LW laser

Grading

Grading varies the optical properties of the material of an MMF cable so that the resulting composition reduces dispersion. Grading minimizes the delay in the propagation of a light beam through the core of an MMF cable. This helps to focus the light beam as it is transmitted down the core of a cable.

Graded-index MMF cableAn MMF cable that has undergone grading is referred to as a graded-index MMF cable. This cable has a higher bandwidth than the simple MMF cable.

Most MMF cables used in networking and data communications are the graded-index type.

For distances greater than 2km (6,561 ft), a graded-index MMF cable requires high-powered lasers. This introduces problems such as modal noise and power fluctuations.

Fibre Channel cable terms

To comprehend SAN characteristics, you need a general understanding of the different properties associated with Fibre Channel cabling. Common Fibre Channel cabling terms to be aware of when configuring the SAN are:

Attenuation Dispersion GBICs Macro bending Micro bending Refraction Wavelength Cone of acceptance Numerical aperture

These terms are defined on the following pages.

Attenuation

Attenuation is the loss of power as a signal travels over a distance and is specified in decibels per kilometer (dB/km). For commercially available fibers, attenuation ranges from approximately 0.5dB/km for single-mode fibers to 1000dB/km for large-core plastic fibers. Attenuation is lessened with higher quality, more expensive, single-mode fibers. It is increased with lower quality, less expensive, multimode fibers.

Power loss can result from:

Light absorption caused by material impurities. Light scattering caused by material impurities or by the defects at the core/cladding

interface, and by the scattering of the molecules of the medium (silica). Macro bends (cable bends beyond the specified radius) and micro bends (cable

wrapping or squeezing). Scattering and reflection at cable splices.

Dispersion

Dispersion is the degree of scattering of the light beam as the beam travels along the fiber optic cable. The different types of dispersion are:

Scattering — Loss of light signal caused by microscopic impurities of the material. Chromatic dispersion — Loss of light signal caused by different wavelengths traveling

at different speeds. By limiting the number of wavelengths of light (as in single mode fiber), the chromatic dispersion is limited.

Modal dispersion — Loss of light signal caused by different light rays traveling different path lengths within the fiber. Some rays follow a more direct route than others and arrive at the destination out of phase. Modal dispersion is characteristic of multimode fiber.

GBICs

The GBIC is a device that converts the electrical and optical signals used with the fiber-optic medium. It contains a laser device that emits a laser signal used for transmission along the fiber optic cable.

The GBICs have two channels, one for each optical fiber within the cable (link). Therefore, each GBIC module is a full-duplex transmission device.

Macro bending

Macro bending is the physical bending of the fiber cable past the specified radius (1.25 to 1.50 inches). As the fiber exceeds the specified radius, the light loses some particles and attenuation increases.

Micro bending and refraction

Micro bendingMicro bending losses occur when the beam does not follow an entirely linear path, such as when a cable is wrapped with a tie or the cladding is squeezed. Micro bends in the axis of an optical fiber can dramatically reduce the transmission of light through it.

RefractionRefraction is the bending of light that takes place at a boundary between two materials having different indices of refraction. Refraction is caused by a change in the speed of light as it passes from one medium to another.

Wavelength and cone of acceptance

WavelengthA wavelength is the distance between any two successive crests (high points) of the light wave and is identical to the distance between any two troughs (low points) of the wave.

All electromagnetic waves are similar; only their wavelengths are different.

Cone of acceptanceEach type of fiber will only transmit light that enters the fiber core cone of acceptance. If a ray hits the core at an angle outside this cone, the light will be reflected. The cone of acceptance parameter is the numerical aperture (NA) of the fiber.

Larger cones have a larger NA, which is also an indication of the relative light-gathering power of the fiber. The cone of acceptance for multimode fiber is larger than that of a single-mode fiber.

Numerical aperture

The NA of the fiber defines which light can be transmitted and the light-gathering ability of the fiber. Imagine a cone coming from the core. Light entering the core from within this cone is propagated by the total internal reflection. Light entering from outside the cone is not.

A high NA gathers more light, but lowers the bandwidth. A lower NA increases bandwidth.

NA has an important consequence. A high NA makes it easier to inject more light into a fiber. A lower NA tends to give the fiber a higher bandwidth. A high NA enables greater modal dispersion by enabling more modes in which light can travel. A lower NA reduces dispersion by limiting the number of modes.

Connectors

Usually, two connector types are required to complete a connection. As a convention, the two types of connectors are referred to as:

Male — The male connector has pins. Female — The female connector has receptacles (sockets) into which the pins of a

male connector can be inserted.

A unisex connector has both pins and sockets.

The connectors available for Fibre Channel interfaces are:

SC connector — This is the standard connector for fiber optic cables. It is a push-pull connector. This means that if the cable is pulled, the tip of the cable in the connector does not move out, which might result in a loss of signal quality.

ST connector — This has a simple plug-in that can be either male or female. Copper connectors — The standard and most commonly used connectors for copper

cables are DB-9 and High Speed Serial Data Connector (HSSDC) connectors. DB-9 connectors are inexpensive and allow the use of copper cabling, which is also inexpensive. DB-9 connectors also allow upgrading a connection for fiber optic data transmission.

GBIC

A GBIC is a plug-in module that can be used to connect both copper and fiber optic devices to a hub or a switch.

You can change or replace a GBIC when a product is operational and running. You can change a GBIC from copper to fiber optic by plugging the copper cable on one side and the fiber optic cable on the other side.

Different GBICs are available for shortwave and longwave cables. A shortwave GBIC is available for an MMF cable and a longwave GBIC is used with an SMF cable.

GBICs use an HSSDC connector for copper devices.

GBIC shortwave

GBIC shortwave is a shortwave version of the GBIC module that supports the multimode fiber. The following table shows the shortwave GBICs specifications.

Feature Details

Compliance Fibre Channel FC-PH-2 physical layer option 100-M5-SN-I

Baud rate 1062.5MB/s

Fiber shortwave

50mm diameter (preferred) or 62.5mm multimode fiber

Laser wavelength

780nm (non-OFC)

Optical connector interface

Dual SC

Distance 50m: 2 through 300m per link (International) 62.5m: 2 through 500m per link (North America)

GBIC longwave

GBIC longwave is a longwave version of the GBIC module that supports the single-mode fiber. Longwave GBICs have the following specifications.

Feature Details

Compliance Fibre Channel FC-PH-2 physical layer option 100-M5-SN-I

Baud rate 1062.5MB/s

Fiber longwave

9mm single-mode fiber

Laser wavelength

1250nm

Optical connector interface

Dual SC

Distance 10km per link (maximizes cable length per FC-AL to 25km)

Gigabit Link Module

Gigabit Link Modules (GLMs) are modular media connectors that mount on hardware interfaces. A GLM, like a GBIC, can be used to connect both copper and fiber optic devices. However, a GLM differs from a GBIC in that it cannot be changed while a device is powered on.

Equipment using GLMs for shortwave can be modified to work with GLMs for longwaves by removing and replacing the GLMs. GLMs can incorporate additional signaling functions and facilities for low-level diagnostics and management functions.

Fibre Channel copper connectors

Fibre Channel copper connectors:

DB-9 Well-known interface Flange-mounted receptacle that has slightly better EMI characteristics

High Speed Serial Data Connector (HSSDC) Unique interface that cannot be confused with existing serial or parallel

interfaces

Impedance control Lower profile suitable for PCI and related applications Contacts immune to stubbing problems common in pin and socket products Higher life cycle

Copper connector considerations

Copper connector considerations:

Use FC-AL hubs that have excellent high-frequency jitter suppression, and low-frequency jitter tolerance.

Protect against potential electrostatic discharge (ESD) problems with the passive copper GBIC.

Avoid crosstalk that can occur if the receiver of the passive GBIC, hub, or switch detects a signal level of sufficient amplitude.

Use the passive copper GBIC only with cable lengths less than 13m. Use the active copper GBIC for cable lengths exceeding 13m. Use an equalized cable with copper cable lengths of 25m or more. Do not use copper cables to interconnect hubs, switches, or devices that have different

ground potentials. Ensure common ground on all chassis (mandatory).

Media interface adapter

A media interface adapter (MIA) is a device used to convert electrical signals to optical signals and vice versa. Although a MIA is mostly used to connect to devices through HBAs, it can also be used with hubs and switches.

A MIA uses the DB-9 connector for copper devices. To connect to optical devices, a MIA uses SC connectors.

MIAs convert Fibre Channel copper to multimode fiber. The MIA receives power from the device through the DB-9 connector. The MIA is useful when extending the distance beyond the 30m copper limitation and connecting a copper interface to a Fibre Channel hub or switch.

MIA benefits

Converts a copper-only HBA to multimode fiber Uses standard dual-SC connectors Extends the distance of the link from the HBA to a hub or switch

MIA disadvantages

Is expensive, adding substantially to the price of the copper interface Is not manageable Does not provide support for the HSSDC copper interface Does not always receive power from DB-9 connectors Is sometimes considered it a "kludge" (awkward or clumsy solution) approach by some

manufacturers Does not help alleviate high EMI from fully loaded, copper-only hubs

Optical connectors

SCThe SC connector has a push/pull snap fit. The duplex SC connector uses the same mating profile as the simplex design. A number of SC suppliers actually clip simplex SC connectors together to form the duplex version. SCs are found in 1Gb/s SAN infrastructure environments.

FCThe FC connector has a screw-on mating style. Primarily used in the telecom industry, the FC is a robust, highly reliable design.

STThe ST (Straight Tip) connector has been a perennial favorite for its termination simplicity and low cost.

MT-RUse a single ferrule that handles two fibers. This is the first of the small form factor (SFF) connector designs. The MT-RJ is a variation of the reliable MT-ferrule connector series, the first major multifiber ferrule design.

FDDI (MIC)This is a ceramic ferrule-based, duplex connector system.

ESCONThis is a ceramic ferrule-based, duplex connector system used in mainframe connectivity systems.

LCThe LC is a SFF ceramic-based connector used with most 2Gb/s SAN infrastructure environments.

MTP/MPOThe MTP/MPO is a multifiber connector design capable of supporting 4, 8, 10, 12 and higher fiber counts.

MMCThe MMC connector is the industry's first viable 72-fiber connector. Using 6 to 12 fiber MT ferrules, the MMC connector finds its way into high-density interconnect applications in the telco and data center cabling environment.

SMCThe SMC connector is based on the MT ferrule and incorporates design features of the ESCON type connector. It has several configuration styles to allow for internal and external applications, resulting in three body lengths on jacketed and unjacketed 12 fiber ribbon cable.

MU connectorAn SFF connector that can be considered a smaller SC style connector. It is based on a 1.25mm ceramic ferrule and is available in simplex, duplex, and higher gangable styles.

Comparing fiber optic and copper cables

SecurityFiber optic cables do not radiate electromagnetic energy. Their emissions cannot be tapped. This makes them a secure medium for carrying confidential data.

FlexibilityAlthough fiber optic cables are actually fibers made of glass, they are easier to work with than copper cables. Fiber optic cables are more resistant to crushing and cutting than copper cables. Their flexibility makes them easier to handle.

DistanceFiber optic cabling supports long distances, but the core size between two nodes must be the same. This limitation applies only when fiber optic cables are connected directly. You can overrule this limitation when fiber optic cables are connected through a hub or a switch.

Advantages of fiber optic over copper cable

High bandwidth EMI immunity

Safety from sparks and short circuits Data security Easy to install and handle More reliable Data transmission to longer distances Lightweight

CostsA copper cable is less expensive than a fiber optic cable. However, the prices of fiber optic cables are becoming more competitive with their copper counterparts.

Transceivers for Fibre Channel

A transceiver is a device that connects cabling to devices on any network or system and makes data transmission possible between devices. Most transceivers have built-in, amplifying circuitry to increase signal strength over long distances. Currently, 1Gb/s and 2Gb/s transceivers are available, with 10Gb/s in development.

A transceiver was designed to provide gigabaud capability for Fibre Channel bandwidth and other protocols that use the same physical layer. This transceiver is the 1.0625 or 2.125Gb/s Serial Optical Transceiver Small Form Factor-Pluggable-2 (SFP-2) 125GHz-SW (2.125GHz-shortwave).

The fundamental design is composed of a:

Transmitter section that consists of a laser and its drive circuit. Receiver section that consists of a photodiode and its accompanying amplification

circuit.

Transmitter signal interface and control electrical interface pins indicate the data rate of the incoming optical and electrical signals.

When high (a logical one), the data rate of the incoming signals is 2.125Gb/s. When low (a logical zero), the data rate of the incoming signals is 1.0625Gb/s.

The Removable Serial Transceiver module is designed to provide 2.125 or 1.0625Gb/s data rate capability for Fibre Channel and other protocols that use the same physical layer.

Cabling and connectors

The appropriate fiber optic cable is a 50/125µ multimode fiber with a LC Duplex connector. The optical receiver can receive input data at rates up to 2.125Gb/s.

The transceiver complies with the 1.0625Gb/s Fibre Channel specification and 2.125Gb/s Fibre Channel standard without an external control signal. The transceiver can be used in applications for data communication networks, telecommunication networks, and other communication networks.

A pluggable module that has a 2 x 10 electrical surface-mount connector assembly with the SFP-2 125GHz-SW transceiver features a serial ID module. The serial ID module can store up to 128 bytes of vital product data. The SFP-2.125GHz-SW transceiver uses a short wavelength (850nm) Vertical Cavity Surface Emitting Laser (VCSEL) source. This source enables data transmission over optical fibers at distances up to 500m at 1.0625Gb/s and 300m at 2.125Gb/s.

The unit is a Class 1 laser-safe product. The optical power levels, under normal operation, are at eye-safe levels. Optical fiber cables can be connected and disconnected without shutting off the laser transmitter.

LC cabling

LC cabling

The bend radius of any cable (electrical or fiber optic) must not be less than 1.5 inches. Additional intermediate optical connections, such as patch panels, should be avoided.

Each such connection causes a certain amount of signal loss ("insertion loss").

Cabling requirements

2Gb/s connections use a smaller form factor than 1Gb/s connections. 2Gb/s to 1Gb/s connections and HSV controller to 1Gb/s switches require new

cables (LC-SC). 2Gb/s to 2Gb/s connections and HSV controller to Fibre Channel drive enclosures

come with a solution package (LC-LC).

LC Duplex connector

The LC Duplex connector is a duplex tight-buffered, multimode, 50/125mm fiber optic cable assembly with LC Duplex connectors at one end and SFF LC Duplex connectors on the other end.

SC Duplex connector

The SC Duplex connector is a duplex tight-buffered, multimode, 50/125m fiber optic cable assembly with low metal SC Duplex connectors at one end and SFF LC Duplex connectors on the other end.

Note: Connector keys transmit and receive polarity only. The connector keys do not differentiate between single-mode and multimode connectors.

Fibre Channel cabling: Learning check

1. Which type of cable uses an RJ-45 connector? Choose the correct answer.

Coaxial cable

Fiber optic cable

Shielded twisted pair cable

Unshielded twisted pair cable

For help, see Copper cables

2. What is a jacket on a fiber optic cable made of? Choose the correct answer.

Silica

Germania-doped silica

Pure glass

An acrylate coating

For help, see Fiber optic cables — Structure and composition

3. Which type of cable supports the longest distances between devices? Choose the correct

answer.

Single-mode fiber optic

Multimode fiber optic

Copper

For help, see Fiber optic cables — Comparing SMF and MFF cables

4. Which connector has a simple plug-in that can be either male or female? Choose the

correct answer.

SC

ST

Copper

For help, see Connectors

5. You can change or replace GBICs when the system is up and running. Choose the correct

answer.

True

False

For help, see Connectors — GBIC

6. Which connector does a media interface adapter (MIA) use to connect to copper devices? Choose the correct answer.

SC connector

ST connector

DB9 connector

DB10 connector

For help, see Connectors — Media Interface Adapter (MIA)

7. Which data rate identifies the speed of incoming high optical and electrical signals from a transceiver signal interface? Choose the correct answer.

1.0625Gb/s

1.1625Gb/s

2.125Gb/s

2.225Gb/s

For help, see Transceivers for Fibre Channel

SAN Fundamentals

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