3.5'' Vs. 2.5'' SAS HDDs: In Storage, Size Matters

2.5” Test HDDs: Hitachi Ultrastar C15K147

Finally, Hitachi's Ultrastar C15K147 is representative of 2.5” high performance enterprise hard drives, offering up to 147GB capacity. This isn’t much, but it's still more than most SSDs. In addition, Hitachi's next generation, with up to 300GB capacity, is only a few months away.

This drive offers the same characteristics as the 3.5” drive: 64MB cache and a SAS 6Gb/s interface. Hitachi uses two platters for this product, and we found that power consumption is amazingly low for a 15,000 RPM drive. A 4.7W idle and and 7.3W peak load is roughly half the power consumption of most 3.5” drives. The C15K147 doesn't run much cooler, though, still registering 59°C versus 61°C and 64°C for the 3.5” drives.

Performance-wise, the C15K147 can't reach the Ultrastar 15K600's 195 MB/s throughput, but it reads and writes data almost exactly at the same speed as the Ultrastar 15K450. Application performance outstrips the 15K450 a bit, while I/O performance is slightly better on the 3.5” drives. However, 2.5” drives have significant advantages over 3.5” models when it comes to storage density in rackmount environments. The space and power envelope required to run four 3.5” drives will allow up to ten 2.5” drives in the same 1U.