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Outlook, Conclusion And Remaining Questions & Answers

Does Power-Saving Technology Kill SSD Performance?
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We were amazed to see these results, as they come at a time when many tech publications are spending a lot of time analyzing the disadvantages of flash SSDs. Flash SSDs such as the X25-E (for servers) and the X25-M (for consumers) have tremendous performance potential—to pick the right wording. But you have to get the appropriate product for your particular applications: high-end SLC flash SSDs are great for I/O-intensive applications, while MLC flash drives provide more capacity at a lower price, but at the cost of decreased write performance and I/O throughput.

Both types of drive may be impaired by block-level fragmentation and/or changes of usage model at some point. It is still up to the user to use her or his SSD in the most efficient way, avoiding fragmentation and eschewing the use of file-system based defragmentation tools, which won’t do any good.

Conclusion: Power Saving Can Reduce SSD Performance

However, our findings are significant, as they can affect users who may not even know they are running an SSD with the brakes on. In short: really fast SSDs that can deliver 200 MB/s or even more of throughput become limited by CPU performance due to power saving mechanisms—or more precisely, they are bottlenecked by a limited availability of CPU time. This became obvious by switching the various power saving options on and off. We found that the sophisticated power saving mechanisms—such as the Active State Power Management for PCI Express, or the deeper C states that switch off entire functional units within the CPU at a transistor level—have a noticeable impact on the performance of our X25-E flash SSD. Obviously, the latency added by utilizing the more complex power saving features is significant enough to have to wait for the system to pick up data.

The conventional power saving techniques, such as Enhanced SpeedStep—which reduces clock speed and voltage during idle or low load periods—showed the least impact. This is also the case for C1E mode (enhanced halt). Thus, we recommend keeping both of these enabled, as they contribute to lowering CPU temperature while reducing power consumption. All of the sophisticated power saving mechanisms are questionable for fast, SSD-powered systems. We believe that it does not make sense to go for a hardcore flash SSD product, just to lose performance on the way due to sophisticated power saving features. Check your BIOS options should your SSD performance not be at the level you expect it.

Remaining Questions and Answers

There are several questions we did not answer within our evaluation, which we’ll briefly cover here:

Why did we use the Intel X25-E?

We used it because it’s the fastest flash SSD currently available. It allowed us to create sequential throughput that exceeds 200 MB/s.

Do the findings affect I/O performance as well?

Yes, but the impact is comparatively small.

Will the results be the same on other motherboards?

We quickly tried a third board, and saw the same results. Depending on the individual implementation of power saving options, and the processors used, the performance difference will vary. However, the same conclusion remains: a fast SSD requires a fast processor to unleash its full performance.

Do power saving options also affect hard drive performance?

No. The fastest hard drives available are still far from reaching 200 MB/s. We benchmarked two 15,000 RPM SAS drives, but could not see a difference as significant as was the case with the Intel X25-E flash SSD.

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  • 7 Hide
    Tindytim , March 12, 2009 7:45 AM
    Articles like this make me wish we could rate articles. Great article!
  • 3 Hide
    Anonymous , March 12, 2009 8:37 AM
    how bout amd???
  • 0 Hide
    hhh1964 , March 12, 2009 9:03 AM
    Next step is to find a workaround.
    I don't yet have a system to experiment with but have a few suggestions.

    How about setting process affinity and raising priority of the processes involved with disk access?
    On my Dell laptop, I use an application called SpeedSwitchXP that makes it possible to manipulate the C-state policies for Demote/Promote-limits on microsecond level. It seems reasonable that introducing a little more hysteresis in the C-state policies would keep the CPU faster between disk operations.
  • -1 Hide
    neiroatopelcc , March 12, 2009 9:17 AM
    Run 4 & 5 for X8SAX show the same stuff disabled (and a capitalization missed) .... mistake?
  • 0 Hide
    neiroatopelcc , March 12, 2009 9:26 AM
    ArticleDo power saving options also affect hard drive performance?


    No. The fastest hard drives available are still far from reaching 200 MB/s. We benchmarked two 15,000 RPM SAS drives, but could not see a difference as significant as was the case with the Intel X25-E flash SSD.


    Btw, does this assessment count for raid usage as well? I'm seeing fairly irregular speeds on my raid 5 (5x500gb) on my ich9r based system. Gigabyte said it was because I was using the raid as a system drive. So I created a raid 0 of 2x500gb drives for windows, but the irregular speeds on the raid 5 remained.
  • 1 Hide
    cedriclam , March 12, 2009 9:35 AM
    Just out of curiosity, will the performance be affected if a dedicated raid card is used to connect the SSD?
  • 0 Hide
    pschmid , March 12, 2009 10:19 AM
    @cedriclam: Hard to say, but I'd guess yes. We will look into this again soon, using different platforms.
  • 0 Hide
    pschmid , March 12, 2009 10:22 AM
    We didn't have two X25-Es to check if this is also the case for RAID setups, but my feeling says yes. The same applies to other controllers, but we'll look into this in greater detail soon!
  • 1 Hide
    Turas , March 12, 2009 10:55 AM
    This may be a case of benchmarks not showing what true real world results would be. Since most things that would truly stress the hard drive performance would most likely also be using more CPU so they would not be in the low power states.

    Just thinking out loud.
  • -1 Hide
    marraco , March 12, 2009 11:14 AM
    Tomshardware dudes:

    Today I feel a deep rant, giving you 5 stars for this investigation.

    Keep doing good work. :) 
  • 0 Hide
    asgallant , March 12, 2009 2:03 PM
    Nice work on the article! I've got a couple of questions though:

    Does this affect I/O performance as well, or is it just throughput?

    and,

    Do you get the same affect on AMD systems?
  • -2 Hide
    KyleSTL , March 12, 2009 2:20 PM
    patrick, what car are you driving in your avitar? (just curious)
  • 0 Hide
    Anonymous , March 12, 2009 3:06 PM
    Does the SSDs support Write Caching (in disk properties), and if so, have you turned it off? It's been my experience with regular HDDs that turning off write caching has an impact on CPU usage...
  • -6 Hide
    Aerobernardo , March 12, 2009 4:44 PM
    Canute24how bout amd???


    For god sake!!! I own an Opteron, but please you AMD spammers are killing us! Who the hell would buy a crappy slow $200 Phenom to pair it up with a $800 SSD?

    Buy a Tata $2500 car and put some 26in wheels on it too!
  • 0 Hide
    ifko_pifko , March 12, 2009 4:53 PM
    AerobernardoFor god sake!!! I own an Opteron, but please you AMD spammers are killing us! Who the hell would buy a crappy slow $200 Phenom to pair it up with a $800 SSD?Buy a Tata $2500 car and put some 26in wheels on it too!

    As far as my knowledge goes, Phenoms II are not slow. ;-) Sure they are slower than core i7, but they are fairly cheap. Not only core i7 can benefit from SSD.
    I'm sure Tom's will test this issue on an AMD platform too. :-)
  • 0 Hide
    Anonymous , March 12, 2009 6:56 PM
    Do MLC flash drives also exhibit the same slowdown with the power saving features turned on?
    I know they are much slower to start with, but do they also get affected equally?
  • 0 Hide
    marraco , March 12, 2009 8:02 PM
    Aerobernardo... Who the hell would buy a crappy slow $200 Phenom to pair it up with a $800 SSD?Buy a Tata $2500 car and put some 26in wheels on it too!
    Somebody who need the fastest SSD, on a limited budget, and found that AMD does not have the energy-saving performance issue (Who knows?. for THAT reason we want to see the AMD benchmarks)
  • 0 Hide
    krazyderek , March 12, 2009 11:37 PM
    please benchmark some of the new OCZ SSD's now that you have a new reference system, i've been dying to see real world numbers for the OCZ apex and especially the VERTEX series! Two drives that claim decent performance without completely emptying my wallet.
  • 0 Hide
    MrCommunistGen , March 12, 2009 11:44 PM
    In the top paragraph of the "Outlook, Conclusion And Remaining Questions & Answers" section the second sentence reads: "...and the X25-E (for consumers)" That should probably be X25-M ;) 

    Otherwise, very interesting article.

    -mcg
  • 0 Hide
    plbyrd , March 13, 2009 12:21 AM
    If you are worried about performance are you going to be running with the power savings stuff anyways?

    To me, the bigger issue is the amount of dependency this setup has on the CPU. It would be interesting to see this same set of tests run through a hardware based SAS or SATA RAID controller on a single drive (no RAID, just a drive).
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