The Generic MLC SSD Problem in the Real World

Based on the Iometer results I knew for sure that there was an issue with random write performance on these SSDs, the only common thread between them being the type of controller (JMicron JMF602) and the MLC flash devices being used (Samsung). But I wanted to see if I could get the high latency writes to appear in a real-world benchmark-able way.


The Samsung SLC controller

 

The first indication that something is wrong actually comes from running the Windows Vista install itself, the MLC drive takes 25% longer to complete the install (let’s just ignore the part about the full install not being fully functional upon completion). Clearly there’s an issue with write speed. I ran into something similar with OS X, but I didn't put it together until now.

The problems are far worse in Vista. While OS X will just pause until the data is written, Vista doesn’t seem to respond well to unusually long file write delays. I haven’t been able to get the Vista install to complete without errors on the OCZ Core drive. One install completed but I was greeted with this error as soon as I hit the desktop:

Trying to reinstall gave me this error even before I booted into Vista:

It looks like the Vista install doesn’t do well with significant delays when writing files to the disk. The only way I could actually get a reliable Vista install on the Core drive was by cloning another drive with a working Vista image on it.

For the next test I tried creating a 200MB archive of pictures:

 

So far, so good. The OCZ Core performs no differently than the rest of the pack. Now let's try creating the same archive, but also extracting one at the same time:

 

Ah-ha! Now we're on to something, the SLC and Intel MLC drives are both around 30% faster than the OCZ Core. Let's try creating the same archive but extracting a much larger one:

  Creating 200MB Archive Extracting 5GB Archive Number of Pauses
SuperTalent (JMicron, MLC) 83 seconds 573 seconds lots
Silicon Power (JMicron, MLC) 128 seconds 632 seconds tons
OCZ Core (JMicron, MLC) 60 seconds 222.7 seconds 20
OCZ (Samsung, SLC) 42 seconds 94.7 seconds 0
Intel X25-M (Intel, MLC) 42 seconds 113.7 seconds 0
Seagate Momentus 7200.2 72 seconds 260.6 seconds 0
Western Digital VelociRaptor 46 seconds 90.9 seconds 0

 

You'll notice a new column called number of pauses; this column is the number of times all disk activity ceased on the system, causing the whole machine to stutter for a moment. You'll also notice that there are zeros in this column, unless the drive uses the JMicron controller. Also note the randomness of the problem, the OCZ, SuperTalent and Silicon Power drives all use the same hardware yet I saw tremendous variations between runs. This is a manually timed test but the rest of the drives didn't vary nearly as much.

It's also important to note that while the Seagate notebook drive performed similarly to the Core, it didn't suffer from the pauses. What this helps illustrate is the nature of the problem, it's very bursty - you get a period of very high performance followed by an abrupt stop. The abrupt stops, as we now know, are these 0 - 2 second write latencies where everything in the system is completely starved of data until the write is complete.


Poor hungry CPU, it just wants to eat. Comic by Laura of www.laurascomics.com

From the CPU's perspective, it expects new data on a nanosecond scale, waiting a full second for anything is deadly for performance.

Another way of quantifying the impact is looking at how long it takes to launch an application when we're in this high-latency write period. I tried extracting the same 5GB archive and launching PowerPoint 2007 or Photoshop CS3 (not at the same time).

  Launching PowerPoint 2007 While Extracting 5GB Launching Photoshop CS3 While Extracting 5GB
OCZ Core (JMicron, MLC) 8.5 seconds 24.3 seconds
OCZ (Samsung, SLC) 2.8 seconds 9.3 seconds
Intel X25-M (Intel, MLC) 3.85 seconds 10.5 seconds
Seagate Momentus 7200.2 21.3 seconds 46.5 seconds
Western Digital VelociRaptor 8 seconds 23.5 seconds

 

All of the drives took longer to launch the applications, but while the SLC and Intel MLC drives still performed in a league of their own, the MLC drives behaved like conventional hard drives. Try running an application while your disk is busy doing something else, or better yet, try running a couple - they take forever. SSDs fix that problem, or at least they're supposed to. These MLC drives don't, at least not always; thankfully the SLC drives and more importantly, the Intel MLC drive don't exhibit this problem.

Delving Deeper A Lack of DRAM or a Lack of Cache?
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  • Alleniv - Wednesday, August 19, 2009 - link

    Hi all,
    I report this new review about X25-M, that takes in consideration a comparative with other SSDs and also with HDDs, with several benchmarks ? http://www.informaticaeasy.net/le-mi...m-da-80gb.h...">http://www.informaticaeasy.net/le-mi...m-da-80gb.h...
    Reply
  • Bytales - Saturday, January 03, 2009 - link

    You said this: For example, let's say you download a 2MB file to your band new, never been used SSD, which gets saved to blocks 10, 11, 12 and 13. You realize you downloaded the wrong file and delete it, then go off to download the right file. Rather than write the new file to blocks 10, 11, 12 and 13, the flash controller will write to blocks 14, 15, 16 and 17. In fact, those four blocks won't get used again until every other block on the drive has been written to once

    By this i understand that a bigger capacity SSD, for instance 320 vs 160 will have more blocks and hence you will need more writes to deplete the number a write cycles the SSD was designed for. So for SSD bigger means even longer lasting. IS this TRUE ?
    Reply
  • lpaster - Wednesday, November 26, 2008 - link

    Can you overclock this SSD? Reply
  • Sendou - Wednesday, February 09, 2011 - link

    There are optimization methods available for SSD's which can mitigate performance loss through genuine usage over time.

    One such is Diskeeper's HyperFast Technology.

    There is a white paper regarding HyperFast available at:

    http://downloads.diskeeper.com/pdf/Optimizing-Soli...
    Reply
  • BludBaut - Thursday, March 31, 2011 - link

    I read the pdf article you linked from Diskeeper.

    Based on the information Anand has given in his articles about Intel's technology, Diskeeper's "whitepaper" sounds like crap advertising by a company who's afraid their technology might be considered not only useless but detrimental to use with SSDs. I'm inclined to agree since Diskeeper's own results show a 4x write loss by just *one* "optimization" while Anand's article clearly suggests that the proper design (which he says Intel has accomplished) eliminates the need for Diskeeper's service.

    Until I find more thorough examination of the facts, Diskeeper's remarks make me distrust them.

    On the other hand, Anand's article definitely sounds not just like a puff piece for Intel, but qualifies in my mind as advertising. Wonder how much money Intel has spent on Anandtech? That's not to suggest that anything is misrepresentative (well, it wasn't meant to sound that way, but keep reading and you'll find the one-sided praise will later be partially retracted and I don't know the end of the story yet), but we all know that advertising always leaves out the negatives.

    (Reviews shouldn't sound like advertisements but anyone who's been reading magazine reviews for 30 years knows that's frequently the case. The reviewer's bills get paid by the manufacturers' of the products he's reviewing. But, the reviewer is objective of course. It's a matter of journalistic integrity. Yeah, I believe that. Don't you?)

    One such negative was the promotion of the life of the drive. "20GB a day for five years"? Anand praises Intel for multiplying that by five to "100GB a day for five years" but then tells us that they'll only guarantee the drive for three years and has the audacity to suggest we'll likely have a recourse "if we can prove" ... -- how is anyone going to prove how many GBs a day they put on their computer? The annoyance of trying to keep track is not something 99% of people would do.

    Did you do the math to see how long it takes to write 100GB to a drive with a write speed of 200MB/s? Eight minutes and twenty seconds is all it takes.

    Well, that's great if all you use your computer for is reading articles, checking the news and sales prices and sending email. The drive should last as long as your computer. But if you love video (who loves video???), it's a different story entirely.

    There's another negative that, though first denied, eventually was acknowledged. More than six months later, Anand reports back and says essentially, 'Intel is still the best but the performance does degrade with time and I don't know why.' If he's explained it since then, I've yet to read it.

    So, for those just reading the article, don't get so encouraged that you start drooling. The article has a tendency to make one think, "What am I waiting for? I want one of these puppies!" Unfortunately, Intel's technology isn't as rosy and bulletproof and Anand made it sound.
    Reply
  • kevonly - Friday, November 21, 2008 - link

    I hope you do some benchmark on Samsung's new 256GB SSD. Hopefully it's as good as Intel's. Reply
  • kevonly - Friday, November 21, 2008 - link

    its read/write speed is 200/160 mb/s. Will it sustain that speed in a multi applications running environment?? Reply
  • kevonly - Friday, November 21, 2008 - link

    sorry

    read/write speed is 220/200 mb/s.
    Reply
  • scotopicvision - Monday, November 10, 2008 - link

    The article was an amazing read, fantastic, and well done thank you. Reply
  • D111 - Saturday, October 25, 2008 - link


    Legacy OS like Windows Vista, XP, and Applications like Microsoft Office 2003, 2007, etc. have built in, inherent flaws with regard to SSDs.

    Specifically, optimizations of these OS for mechanical hard drives like superfetch, prefetch, etc. tend to slow down, rather than help performance and is unnecessary to speed up reads in an SSD, but slow it down with unnecessary writes of small files, which SSDs are slower than a regular hard drive.

    Things like automatic drive defragmentation with Vista does nothing for SSDs except to slow them down.

    Properly optimized, even low cost 2007 generation SSDs test out as equivalent to a 7200 rpm consumer grade drive, and typical SSDs made in 2008 or later tend to outperform mechanical hard drives.

    The tests done here have done nothing to "tweak" the OS to remove design hindrances to SSD performance, and thus, have no validity or technical merit.

    The test, as presented, would be similar to installing a 19th century steam engine on a sailing ship, and observing that it is rather slow ---- without mentioning the drag and performance hits caused by the unused sail rigging, masts, etc.

    See the discussion here for a detailed discussion of SSD performance tweaks and what it takes to make them perform well with legacy OS and Applications.

    http://www.ocztechnologyforum.com/forum/forumdispl...">http://www.ocztechnologyforum.com/forum...display....

    Reply

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