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What criteria do you use when defining a server connection?

I'm trying to realize a storage infrastructure for our customer. This structure consists of 3-4 large SANs with a classic switch and each is interconnected with other SANs via iFCP (example Nishan). Other servers are connected via iSCSI to a SAN.

My question is, what criteria do I use to define what a server can use as a connection via FC (SAN) or via iSCSI? In other words, in your opinion what are the key or keys factor to discriminate the use between first or second topologies?


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The SAN to SAN protocol is probably going to be FCIP, not iFCP.

The first criteria for iSCSI connectivity is availability of adapters/drivers for iSCSI. Next comes I/O performance. If I/O performance is relatively small, then iSCSI may work out for you for the least total cost (with a large number of Windows systems). Next comes CPU speed, it helps a lot to have high speed (2.0 Ghz and up) to handle TCP traffic. If CPU speed is less than a Ghz -- and you are using Gigabit Ethernet for iSCSI, then you need to find an iSCSI adapter with TCP offload technology or you may saturate the system CPU.

Finally, you need a bridge/router product for the Ethernet/iSCSI to FC junction for those iSCSI hosts.

There are companies doing what you are talking about, you are not crazy. There are a lot of details to work through, however. Here is a short list of items to include in your analysis:

Network speed
I/O rates for servers
CPU speeds for servers
Available iSCSI drivers/adapters
Available TCP offload adapters
Bridge/router performance
Expected applications and traffic levels for iSCSI to FC storage

Regards,
Marc

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This was first published in November 2002

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