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

Diminutive 2.5” form factors are favored in the enterprise storage world for many reasons, but how do high-end 2.5” SAS drives compare to the established 3.5” products when it comes to performance and power? We requested some drives and did the analysis.

With all of the hype surrounding SSDs (solid state drives) these days, you might think that hard drive technology is already dead. Indeed, flash-based storage will certainly replace high-end hard drives in the months and years to come. One of the first victims will be the 3.5” form factor in enterprise applications. Specifically, 10,000 and 15,000 RPM SAS drives will be replaced by 2.5” drives. We compared both form factors at 15,000 RPM.

While 3.5” desktop and 2.5” notebook drives are very different in most things, save recording density, there are significant similarities between 3.5” and 2.5” enterprise hard drives. These share spindle speeds and capacity points for a reason. Internally, 2.5” and 3.5” enterprise drives are based on the same platter diameter. The actual platters still differ, though, since a higher spindle speed requires more solid platters.

The main difference between the two form factors can be found in their total capacities. The 3.5” form factor allows more platters to be crammed into a roughly 26 mm z-height. Four platters can create 600GB, 15,000 RPM, 3.5” SAS hard drives, while a comparable 2.5” model runs on only two platters. A 2.5” enterprise drive running at only 10,000 RPM is usually based on three platters.

A smaller drive requires less power to operate because there's less mass needing to be moved. But how do 2.5” high performance drives compare to their 3.5” brothers? We grabbed several Hitachi enterprise drives and ran some tests.