Storage Basics: Choosing a RAID Controller Page 3


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External Host-Based

The other type of host-based RAID isn't really RAID at all. External host-based offerings are commonly described as "just a bunch of disks," or JBOD enclosures. A JBOD system is not configured as a RAID setup, and therefore we have elected to not to cover any specific JBOD offerings for this piece. For those interested in learning more, the DF2000J from LSI Logic and theFS4100 Fibre to SATA JBOD from Adaptec are two JBOD products worthy of consideration.

External Controller-Based

Meanwhile, on the external controller-based front, iSCSI, a flexibly routed storage technology, is gaining momentum and garnering market share. Fibre Channel currently dominates this space, however. To date, Network Appliance is the lone player in the iSCSI RAID arena.

"The problem that iSCSI currently is encountering is that Fibre Channel's not standing still," Cox says. "They're bringing the price differential down on Fibre Channel host adapters and switches to a point where iSCSI's losing some of its value proposition in terms of cost." Cox sees value in iSCSI despite its slower speed, as "to me the primary value proposition of iSCSI, until it gets to be 10 Gigabit, will be interoperability."

One external controller-based product banking on this interoperability is Digi-Data's STORM family of RAID controllers. STORM Digi-Data CEO Bill Tomeo pins STORM's modular architecture as its main strength. "The STORM controllers house eight completely independent channels in one box," Tomeo says. "Each 1U box has eight independent Fibre Channels on it, so what we've done is eliminate the catastrophic failures that can occur in a back plane." Controllers typically have controller boards that share a common back plane, which presents a problem should a catastrophic failure occur, he explains.

SAN and NAS offerings also fall into the external controller-based category. For more information about SANs and NAS, check out last month's article.

With five types of RAID controllers and countless vendors peddling their wares, what's an enterprise to do? Bert sums up customer considerations best: Ultimately, "the choices of ATA/SATA, SCSI, or Fibre Channel solutions will depend on the desired trade off between performance, connectivity, reliability, scalability, capacity, and cost."

Feature adapted from ServerWatch.

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