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

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

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.

Display all 4 comments.
  • 1 Hide
    lloydie_p , 9 May 2010 08:39
    "you can easily imagine that a simple RAID with four 3.5” drives could be replaced by six to ten 2.5” drives".

    With the drives mentioned at max throughput 10 x 2.5(15K) would draw 73 watts versus the 59 watts of the 4 x 3.5(15K 600GB) an considering the 4 x 3.5 would = 2.4TB of space and 10 x 2.5 only 1.4TB; unless no one considers capacity I don't see how 2.5 inch drives make for the best compromises.

  • 0 Hide
    andybird123 , 10 May 2010 23:34
    this article does talk about the trade off on throughput and performance per watt, versus raw capacity, but you are right, it's a trade off - at the same price point you can either go for 1.4TB of very fast storage space, or 2.4TB of fast storage

    if you were mainly interested in storage space you could get 4 x 1TB 7200rpm SAS drives for around the same price
  • 0 Hide
    shanky887614 , 10 August 2010 00:52
    this is not realy a valid test

    2.5inch drives where originally designed for laptops hence the small form factor and low power

    so it makes sence they will lose to speed and capacity of there 3.5 inch cosins
  • 0 Hide
    BulkZerker , 11 August 2010 23:53
    shanky887614this is not realy a valid test2.5inch drives where originally designed for laptops hence the small form factor and low power so it makes sence they will lose to speed and capacity of there 3.5 inch cosins


    Howso? Really the future for mass server storage seems to be migrating to 2.5" so it makes sense to see what the tradeoff is.

    Also, everyone who is reporting the spammers please mark them down as well as reporting them so people know they've been reported.
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