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Fibre or SCSI RAID for SAN?

A look at cost and performance issues surrounding a decision to use Fibre Channel or SCSI for RAID.

By Rick Cook

Since most storage area networks (SANs) use Fibre Channel networking, it seems logical to use a RAID array built around Fibre Channel rather than the more familiar SCSI interface. In fact, it is logical. Sometimes. But cost, availability and other considerations can affect the logic as well.

Availability isn't nearly the problem it was a year ago. More and more RAID manufacturers now offer Fibre Channel RAID arrays, usually with capacities and features aimed at the SAN market. The limiting factor is compatibility with the rest of your SAN system. Since SANs still have some compatibility glitches, you need to make sure that your SAN vendor will support your proposed Fibre Channel array. Don't neglect to check support from your storage management software as well.

The cost issue depends largely on whether you plan to reuse existing RAID arrays or not. Since almost all RAID installed today is SCSI, using SCSI arrays with a Fibre Channel adapter is definitely cheaper if you plan to reuse what you have now. This is especially attractive because it doesn't keep you from converting to Fibre Channel arrays later.

Fibre Channel RAID arrays are generally more expensive than their SCSI counterparts. The SCSI market is both mature and highly competitive, which helps hold down prices. However, SCSI arrays aren't necessarily very large--or even present at all--in the kind of high-capacity, high-reliability, high-throughput arrays that work best to support SANs.

Performance may be the deciding factor, but don't automatically assume that a Fibre Channel array will be faster than a high-end SCSI array, in spite of the difference in theoretical throughputs.

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About the author: Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.

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