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As disks get bigger, and continual uptime becomes even more of a requirement, disk subsystem vendors are coming up against the limitations of shared protocols like Fibre Channel Arbitrated Loop (FC-AL) used to connect drives within a JBOD.
Addressing a JBOD's latency and availability issues, disk array vendors Network Appliance and Compaq (i.e., HP) have adopted or are evaluating Vixel's InSpeed, an embedded chip that gives switching capabilities to drives on an FC-AL loop.
Other vendors evaluating InSpeed include NEC, Exabyte, ADIC, JMR, BlueArc, and Nexsan.
At issue is drive latency, says Arun Taneja, senior analyst at the Enterprise Storage Group. In a typical JBOD configuration, "to get to the last drive on a loop, you have to go through all the drives before it." By connecting the drives in a switched bunch of disks configuration, or SBOD, as Vixel calls it, you can access that drive directly.
Availability is a factor too. In a JBOD, if one drive goes down, "you have to isolate the entire tray," Taneja says.
Thus far, vendors resisted switching back-end drives for cost reasons. But according to Taneja, the Vixel chip is inexpensive. "I can't imagine why a company wouldn't want to use an SBOD-like chip," he says.
This was first published in July 2002