SAN

SANIT423(d)SAN

What is a SAN?According to the Storage Networking Industry Association dictionary a storage area network (SAN) is any high-performance network whose primary purpose is to enable storage devices to communicate with computer systems and with each other.

The most interesting things about this definition are what itdoesn'tsay:

It doesn't say that a SAN's only purpose is communication between computers and storage.

It doesn't say that a SAN uses Fibre Channel or Ethernet or any other specific interconnect technology.

It doesn't say what kind of storage devices are interconnected.Disk and tape drives, RAID subsystems, robotic libraries, and file servers are all being used productively in SAN environments today. Conventional client server computer system VS SAN environment

4What are the Market Drivers for SANs?The limitations in speed, distance, and connectivity of SCSI technology prompted the search for an alternative method to access storage devices. The need for LAN-free backups and data sharing started the initial move toward SAN technology. These necessities and the desire to keep all data on-line and accessible 24 hours a day to an increasingly global and/or Internet-based user population are driving current adoption.

Market Drivers:Backup Capacity: Increasing data storage requirements and the need for 100% availability of applications have overwhelmed SCSI backups across the LAN.Capacity Growth: IDC and Gartner Group estimate that data is growing at a rate of over 85% annually. To put this in perspective a 750GBSystem Flexibility/Cost: SANs are storage-centric networks that provide easy scalability, allowing servers or storage to be added independently of each other.Availability/Performance: The use of a storage data transmission protocol like SCSI permits the transfer of large amounts of data with limited latency and overhead.

5Why are Storage Area Networks Needed?Traditional means for connecting servers and storage can no longer satisfy today's requirements for fast access to massive amounts of data. SCSI technology uses parallel cabling which severely limits speed, distance and the number of attached storage devices. Configuring SCSI (Small Computer Systems Interface) connections to support terabytes of data is impractical. In addition, traditional server/storage connections make the server the exclusive owner of its attached storage. As computing environments move from a server centric to data centric model, access to shared data resources becomes critical. Storage Area Networks are an enabling technology that allow storage resources to be shared in order to provide continuous, faster, easier access to data.What are the Benefits of a SAN?Availability:A single copy of data is accessible to any and all hosts via multiple paths.

Reliability:Dependable data transportation ensures a low error rate, and an ability to recover from failures is provided.

Scalability:Servers and storage devices may be added independently of one another, and do not depend on proprietary systems.

Performance:Fibre Channel (the standard method for SAN interconnectivity) has a 100MB/sec bandwidth and low overhead, and it separates storage and network I/O.

Manageability:Emerging software and standards for both FC-AL and Fibre Channel fabric allow single centralized management and proactive error detection and correction.

Return On Information Management:Due to increased redundancy and superior manageability, as well as the ability to add storage and servers independently of one another SANs provide a lower cost of ownership and a Higher Return On Information Management (ROIM).When should I use a Switch versus a Hub?Hubs: Hubs are perfect for small, entry-level environments and systems. The typically cost less and offer a lower throughput the switches.

Switches: Data-intensive, high-bandwidth applications such as backup, video editing, and document scanning can make full use of switches. Due to their redundant data paths and superior manageability switches are also perfect when high availability is required.Reasons to use Switches instead of Hubs in a SANSwitches provide several advantages in a SAN environment.Failover Capabilities:In a switched fabric, in the event that a single switch fails, other switches in the fabric remain operational. A Hub based environment typically fails if a single hub on the loop fails.Increased Manageability:Switches support the Fibre Channel Switch (FC-SW) standard, which makes addressing independent of the subsystem's location on the fabric and provides superior fault isolation and high availability. FC-SW also allows host to better identify subsystems connected to the switch.Superior Performance:Switches offer "multiple-transmission data flow", in which each fabric connection can simultaneously maintain a 100MB/sec throughput. A hub offers a single data flow with an aggregate throughput of 100MB/sec.Scalability:Interconnection switches provide thousands of connections without degrading bandwidth. A hub-based loop is limited to 126 devices.Availability:Switches support the on-line addition of subsystems (servers or storage) without for re-initialization or shutdown. Hubs require a Loop Initialization (LIP) to reacquire subsystem addresses whenever changes occur on the loop. A LIP typically takes 0.5 seconds and can disable a tape system that is in the process of doing a backup.

How does a SAN differ from a LAN or WAN?A SAN is similar to a LAN, in that it is a methodology of connecting systems together with standardized hardware and software protocols. A SAN differs from a LAN is two main ways.

Storage versus Network Protocol:A LAN uses network protocols that send smaller "chunks" of data with increased communication overhead. This reduces bandwidth. A SAN uses storage protocols (SCSI) that sends larger "chunks" of data with reduced overhead and increased bandwidth.

Server Captive Storage:LAN based systems connect servers to clients, with each server owning and controlling access to its own storage resources. Storage must be added to a server rather than directly to the LAN. A SAN allows storage resources to be added to the network enabling any server to directly access storage resources.

What is Fibre Channel?Fibre Channel is a standards-based, gigabit transport that is optimized for storage and other high-speed applications. Currently implemented in 1 gigabit (200MBps full duplex) speed, Fibre Channel will support up to 400MBps full duplex transfer speeds in the near future. There are three topologies based on Fibre Channel - point to point, arbitrated loop and fabric. Arbitrated loop and fabric provide the underlying infrastructure of most SAN implementations today. Fibre Channel supports high speed transport, long distances (up to 60 km), and up to 16 million devices in extended network configurations. By introducing the scalability and flexibility of networking to the server/storage relationship, Fibre Channel is enabling new storage applications for clustering, disaster recovery, and shared resource requirements.What is The Difference Between SAN and NAS?Storage Area Networks (SAN) and Network-attached Storage (NAS) are similar, in that they both represent a convergence of storage and networking technologies. However, they are also entirely different. NAS products, such as Network Appliance Filers and Auspex servers are storage devices fronted by a thin server client that is directly attached to the messaging or public network. These products tend to be optimized for file serving purposes only. Storage Area Networks are separate networks dedicated to storage devices and traffic. SANs provide greater flexibility and additional functionality over a NAS. However each of these approaches has their merits, it is generally agreed that SANs represent the future of storage connectivity. NAS devices will continue to perform their specific functions but shall migrate, over time, to the Storage Area Network model.Referenceshttp://www.snia.org/education/storage_networking_primer/san/