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July 15th, 2009 08:00

On what protocols do SAN and NAS work??

Hi,I'm Nikhil and am pursuing my course on Storage foundation and Storage Network Design ( EMC certified).Please explain me the protocols

on which SAN and NAS devices work( In detail pls).

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274.2K Posts

July 17th, 2009 09:00

Greetings Nikhil,

You have asked a really good question here, however the detailed answer is really far to long to include everything here. The short answer is that FC SANs utilize primarily the Fibre Channel Protocol. This is a very high performance protocol used in dedicated data access environments e.g. relatively short distance between server/client and data.

NAS uses predominately Network File System (NFS) in the UNIX/Linux environment and Common Internet file System (CIFS) in the Microsoft Windows environments. There are several hybrid protocols used in this environment too e.g. Multi-Path File System (MPFS) and internet SCSI (iSCSI) being most prevalent with others appearing quickly, FCoE as an example. The NAS protocols are based upon the Internet Protocol base for transport with high level protocols Transmission Control Protocol (TCP) and User Datagram Protocol being used for specific application interfacing. However FCoE allows for the SAN traffic to be natively transported over an Ethernet infrastructure and is an emerging technology for Enterprise Data Centers.

This is merely scratching the surface on the complex subject of protocols used in attaching clients/servers to storage.

I hope this helps out.

Regards

Si

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274.2K Posts

January 5th, 2010 14:00

Hi Nikhil,

Simon did a great overview of the protocols implemented in SAN and NAS. I would like to expand from the SAN side since it's my area of expertise.

The four basic protocols covered are Fibre Channel, iSCSI, FCIP and FCoE.

Fibre Channel is a serial data transfer interfaces. It operates over copper or optical fibre and is the traditional protocol used in Storage Area Networks (SAN). Through it SCSI commands are encapsulated and transported over Fibre Channel Frames. Fibre Channel networks are very efficient because they ensure error-free delivery of packets. This in turn means they lack IP capabilities such as retransmission of lost packets. In oder words Fibre Channel doesn't expect packets to get lost resulting in a distance limitation. In part due to these limitation new protocols have been developed leveraging the existing IP protocol.

iSCSI is one of the protocols used for SAN communication. The protocol uses IP instead of Fibre Channel to encapsulate and transport SCSI frames. The greatest advantage of iSCSI is IP equipment can be leveraged in the data centers. iSCSI require either regular NICs with an iSCSI initiator software, or iSCSI HBAs. On a native solution the storage array must have native iSCSI and everything from host to storage is IP based. In a bridged solution the host is IP based and storage FC based, the switch translated between the two.

FCIP is another solution that uses the IP protocol. It's used mostly for distance extension communication. Since Fibre Channel has distance limitations, this protocol uses IP to transport FC frames over long distance. The FC frame are encapsulated in the IP frame by an FCIP router and then sent to another FCIP router which in turn de-encapsulates them. FCIP can be used for merging fabrics or keeping them separate.

The newest SAN protocol is FCoE. FCoE emerged as a consolidation solution. With evolution in Ethernet bandwidth (10 Gbps) speeds are almost as fast as FC. FCoE promises to improve communication by removing TCP/IP protocol from the protocol stack and transmitting Fibre Channel only over Ethernet. This results in a very efficient frame with little overhead. The idea is to transmit IP, FC, and other protocols through the FCoE infrastructure, resulting in less cables, and equipment in general.

I hope the overview helps in clarifying the different protocols and their uses. For more information take the SAN Storage Protocols E-learning course or for advanced implementation and configuration the Advanced SAN Implementation Workshop.

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