iSCSI is an interesting approach to doing block I/O over IP networks. NAS does file I/O over IP networks. The idea behind iSCSI is to try and do what NAS does not do well -OLTP over IP networks. It is very early in the game for iSCSI and right now, the performance relegates it to a particular market segment. At some time, TCP/IP accelerators (special NIC cards with processors, buffers, and other custom logic) will be available to help in performance but at a cost and probably an infrastructure change to a separate network.
Additionally, IP based storage is faced with the IP security issues that exist today. So I would watch iSCSI carefully to see when it matures and the performance, cost, and security are acceptable for your specific application. One size does not fit all. Meanwhile, FC based storage is still high performance and relatively mature.
Evaluator Group, Inc.
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This was first published in December 2001