Beware of Big Disk Drives

As disk drive capacities keep going up, storage managers need to keep in mind how they will recover the data in case the drive fails. That's especially true of today's ATA drives, which tip the scales at 320GB, and fail relatively frequently.

Even when drives are RAID protected, it can take several hours to rebuild from a drive failure. Randy Arnott, RAID architect with startup RAIDCore, estimates that it would take 10,000 seconds, or 2.7 hours, to rebuild a single drive in an eight-drive 1TB RAID set, assuming rebuild rates of about 100MB/s.

Granted, "that's still better performance than most SCSI arrays," Arnott says. But considering that today's biggest SCSI drive (146GB) is less than half the size of today's largest ATA drives, you are limited in how big of a RAID set you can build--and consequently, how long it takes to recover from a failure.

There are also those that worry about a second disk failing before a RAID set has been rebuilt. That concern is behind Network Appliance's recent announcement of RAID-DP, which stands for dual parity. By adding a second "diagonal parity" disk drive into the RAID set, RAID-DP "lets us withstand a double disk failure and keep on running," says Mark Santora, NetApp senior VP of marketing. This in turn, "allows us to increase the reliability of currently inferior technology [i.e., ATA drives] and move them into the primary storage domain."