The 2.5" hard drive for professional applications is still a new product category. We took a look at Seagate's first 2.5" Ultra320 Savvio hard drive some time ago, which also left us with a good impression. All 2.5" SCSI drives spin at 10,000 RPM today and thus cannot deliver the same performance level that you would receive from a 3.5" drive at the same spindle speed; the outer areas of a 3.5" model rotate at a faster absolute velocity and thus allow for better data transfer rates.

The advantage of smaller hard drives does not lie in capacity either, as the maximum still is 73 GB today, while 3.5" enterprise class drives hit 300 GB a long ago. In many environments, processing capacity or energy efficiency have become important issues. The more hard drives you deploy, the more performance you can harvest in return - given a suitable infrastructure. While I/O performance is a key issue, a large number of 2.5" drives will be able to outperform most 3.5" drive arrays as well. At the same time, 2.5" drives consume clearly less than half the energy that any 3.5" drive requires. When it comes to performance per watt (I/Os per Watt), the 2.5" form factor delivers very good results.

If capacity is what you need, 3.5" 10,000 RPM drives would not necessarily be our primary choice either, because 3.5" SATA drives provide 66% higher capacity with acceptable performance levels (500 rather than 300 GB per drive). Most hard drive makers offer 24/7 SATA drives today and cost per drive is down to a minimum, so the remaining reliability issues can be attended by buying spare drives for immediate replacement.

The 15,000 RPM drive category still serves a need , because it is the only choice that will offer both the highest transfer rates and I/O performance per drive.