SANs rely on either Fibre Channel technology, which provides high bandwidth (2 Gbps) linking storage components, switches and HBAs, or iSCSI technology based on standard IP topologies. SANs were initially proprietary Fibre Channel architectures; but iSCSI is the new kid on the block, generally offering a lower-cost, if somewhat slower (1 Gbps) alternative. Either option can incorporate legacy SCSI devices. There may be some performance degradation with legacy drives, but the ability to maximize existing capital investments can strengthen the business case.
A solid design should rely on dual (redundant) switches with ISL (interswitch links) and dual HBAs to provide maximum uptime for connections between storage subsystems. (For more information on the technical pros and cons, see "iSCSI SANs"; and "High on Fibre".)
There's a lot of talk about proprietary versus open standards for SAN architectures. In an ideal world, a Fibre Channel SAN would work with storage and network components from any vendor, letting you integrate legacy storage and new components as needed. The FC SAN industry is not quite there yet; CIM/OM (overlapping with Bluefin) and SMI-S are the leading FC standards. The Storage Networking Industry Association--whose members include Brocade Communications Systems, Cisco Systems, EMS, Hewlett-Packard, Hitachi, IBM, McData Corp. and Nortel Networks--continues to work on storage interoperability. Meanwhile, the IEEE is weighing in with its Storage Systems Standards Committee. The iSCSI vendors, for their part, are also pursuing interoperability--the Internet Engineering Task Force has a working committee dedicated to IP Storage specifications, producing RFC 3347 back in July 2002.
If you need the 2-Gbps speed of Fibre Channel, expect to limit your FC implementation to a subset of vendors whose equipment has been proven to play well together. When talking through RFPs (requests for proposals), be sure to get references from customers detailing their environment and legacy components.
Bottom line: SANs are expensive and not easy to implement. Few shops have any in-house FC experience, and few training centers or schools offer FC curricula. Thanks to basic economics, you can bet that any FC consulting you bring in-house will be dear. Because iSCSI relies on conventional IP, this type of SAN will be more familiar to your staff. But you're still likely to need outside help.
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