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Conclusion

3.5" Vs. 2.5" SAS HDDs: In Storage, Size Matters
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Clearly, even the latest 2.5” Ultrastar C15K147 doesn’t stand a chance against the 3.5” Ultrastar 15K600 if you look at performance. This is because of the 3.5" model's higher data density and more aggressive performance. However, the 2.5” drive shines when it comes to power consumption, requiring half or even less power than the 3.5” drives, while performance differences aren’t even remotely close to the 50% or higher difference in power consumption.

In general, 2.5,” 15,000 RPM SAS drives will deliver 25% less performance than 3.5” drives, but efficiency increases at least twofold. Our results here are specific to Hitachi's drives, but we would expect similar results with Fujitsu or Seagate drives, although the performance results would have been different.

The performance "issue" with 2.5" drives can be managed through adjusting the drive count. Two 2.5” SAS drives in RAID will outperform one fast 3.5” SAS drive in every workload. At the same time, the power required won’t be higher and capacities may be similar.

If you take our results to the next level, you can easily imagine that a simple RAID with four 3.5” drives could be replaced by six to ten 2.5” drives. These would not consume more power than the 3.5” models, but resulting performance would be 50% to 2.5x higher, depending on the specific configuration. Meanwhile, power consumption will remain below the level of the 3.5” RAID.

All that’s left to consider is cost, and this has to be contemplated carefully. Performance storage may offer the best cost effectiveness when using a small number of SSDs, but as soon as you need capacity, flash memory might quickly become too expensive. That's when you’ll turn to arrays with 15K drives. For best price/capacity, 3.5” drives at 7,200 RPM are probably the most sensible choice unless you also need a certain performance level. In that case, you'll find best compromises with 2.5” hard drives.

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  • 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.