Types of Storage…..

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The three fundamental types of storage are….

• DAS (Direct Attached Storage)• NAS (Network Attached Storage)• SAN (Storage Area Network)

All three Storage types evolved over the years, Storage requirements and technology advancement led to one another. In other words DAS led to -> NAS and in turn NAS led to -> SAN.

Types of Storage…

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Typical DAS Storage solution

Types of Storage…

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Typical SAN Storage solution

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Types of Storage….

DAS as its name implies is simply primary storage that is designed to be used by one and only one computer.

Advantages:

Great for Mainframes and OLTP type high data intensive requirement.

Disadvantages:

DAS cannot share unused resources or data with other servers, and therefore it is also called island of information.

DAS typically have limited scalability, Server has to be rebooted, creating downtime during the installation process.

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Types of Storage….

In the early 1990s, Windows and UNIX server vendors decided that they were going to replace the mainframe. Within a few years they launched a project called “Mainframe Replacement Program".

As we discussed in the earlier side, DAS was primarily used for Mainframe computing b'cos of the Block-storage access, but due to many disadvantages such as unable to share the disk and limited scalability issues, it led to the development of "SAN".

SAN is basically an extension of DAS, but more robust, shareable storage with highly scalable.

SAN provides block-level access to centralized storage. SANs were created in large part due to earlier technology limitations associated with DAS & NAS

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Difference between NAS & SAN

Traditional Differences

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Difference between NAS & SAN

Block Oriented Difference between NAS & SAN

The Wires being used:• NAS solutions utilize TCP/IP based networks, such as Ethernet• SAN solutions use Fibre Channel connections (Fiber/Copper)

The Protocols being used:• NAS solutions use file level protocol (CIFS/NFS) and now also SCSI over IP called iSCSI Protocol over standard Ethernet networks• SAN solutions utilizes Fibre Channel encapsulated SCSI setups

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FC-SAN communicates at the block level, with requests over the "wire(fiber/copper)" like :

•Read-block-thirty-four or •Write-block-five-thousand-and-two

NAS communicates at the file level, with requests over the "wire (Ethernet)“ like:•Create-file-MyHomework.doc or •Read-file-Budget.xls

Difference between NAS & SAN

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Mount:Client -> The client sends the pathname to the server and requests permission to access the contents of that directory.Server-> Checks whether the path exists in the /etc/fstab Or /etc/dfs/sharetab. If it exists ? YServer-> Returns a "File handle" to the client (file handle contains-filesystem type, disk ID, inode, security info.Client-> Creates a In-kernel vfs mode (virtual file system) and mounts it to a folder/directory.

Directory access Protocol:Client-> sends RPC messages to the server to manipulate files & directories. File is accessed by "lookup" RPC call. This returns :a. File handle - using this file handle other parameters are passed such as -read (handle, offset, count)this function will read count bytes from location offset in the file referred to by handle. b. attributes - such as size.

NFS uses 2 protocols - Mount & Directory file access protocol.

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Evolution of SCSI standards…