Bigger data volumes call for bigger disk drives, right? Well, storage managers are finding it's not always that simple. Sources say fatter drives can thin out performance. (See Capacity Considerations.)
To start at the top: There's a move among vendors to upgrade existing drives inside storage systems to faster, higher-capacity ones. Pillar Data Systems, for instance, has added 750-Gbyte SATA drives from Seagate to its Axiom Systems, which up to now have used 500-Gbyte Hitachi SATA drives. "We have increased the our overall capacity within a single system by 50 percent," Pillar CEO Mike Workman told Byte and Switch earlier this week. (See Pillar Pushes Provisioning, Capacity.)
And 750-Gbyte drives are just an example. With 1-Tbyte SATA drives from Hitachi and Seagate on the boil, the ante has been upped. Last week, Nexsan reported the adoption of Hitachi's 1-Tbyte drives in its storage arrays, upping capacity 33 percent. (See Nexsan Deploys Tbyte Drives and Idealstor to Add 1-Tbyte Disk.)
Some analysts warn that swapouts can stymie performance. "It's not that seek time, access time, or latencies change as drive capacity increases," says Arun Taneja of the Taneja Group consultancy. "All that is going to be the same. In fact, the native performance of a drive may even improve. But it's a fundamental truth that as you add more capacity behind a single drive, designing for system performance without increasing cost becomes more challenging."
"Higher capacity drives have the same number of heads as lower capacity drives," says one storage consultant, who asked not to be named. "So the number of heads per gigabyte declines, and if nothing is done to increase controller performance, performance declines."