A Lack of DRAM or a Lack of Cache?

The high latency random write issue is annoying enough that it'd force me not to recommend any of the non-Intel MLC drives on the market today, regardless of how attractive their pricing may be. High performance with caveats isn't exactly high performance to me.


Intel's controller (left) + DRAM (right)

That being said, the root of the problem is still unknown. My first thought was that it was because the MLC drives had no DRAM buffer, and if you'll notice, Intel's MLC drive does have a DRAM buffer. I asked Intel about this and it turns out that the DRAM on the Intel drive isn't used for user data because of the risk of data loss, instead it is used as memory by the Intel SATA/flash controller for deciding exactly where to write data (I'm assuming for the wear leveling/reliability algorithms). Despite the presence of the external DRAM, both the Intel controller and the JMicron rely on internal buffers to cache accesses to the SSD.

Finding good data on the JMicron JMF602 controller is nearly impossible, but from what I've heard it's got 16KB of on-chip memory for read/write requests. By comparison, Intel's controller has a 256KB SRAM on-die. And I'm going to go out on a limb and assume that given Intel's experience with CPU caches, that its SRAM implementation is probably very well done.

With the JMicron based solutions, if you try and write too much to the drive (and trust me, it won’t take a lot) and the buffers get full, the controller tells the system that it’s not ready to write more data and you get a pause.

When you cause the JM602’s internal buffer to overflow, your system runs in bullet-time. Applications take much longer to launch and close, windows take longer to appear, and there are distinct pauses in anything you want to do that involves the disk. Want to send an IM? Well, that writes to an IM log - you can expect a pause before you can send your IM. Loading webpages is the worst, reading from and writing to the cache wreaks havoc on these cacheless MLC drives. Just for kicks I tried loading AnandTech while I was extracting a 5GB file on the SuperTalent 60GB MLC, it took over 10 seconds for the website to load. Once the JM602 was free to fulfill the read request, the website just popped up - but until then it was like my DNS was failing. It’s a lot like what happens to your notebook if you try and do too much, the disk quickly becomes a bottleneck.

Thankfully, as we've already seen, this problem is only limited to JMF602 based MLC drives. The SLC drives and the Intel MLC are totally fine, so while I'll include these problematic MLC drives in today's comparison, let me state now that I would not purchase one.

JMicron's roadmap shows a new controller next year with an integrated ARM core as well as support for external DRAM, which could alleviate these problems, but until now the controller, and drives based on it, aren't worth it. You get a much better overall experience out of a conventional mechanical disk drive, and much better performance from the Intel SSD or any of the SLC solutions on the market.

The Test

CPU: Intel Core 2 Quad Q9450 (2.66GHz)
Motherboard: Intel DG45ID
Chipset: Intel G45
Chipset Drivers: Intel 8.1.1.1010 (Intel)
Memory: Corsair XMS2-8500 1066
Video Card: VisionTek Radeon HD 4850
OS: Windows Vista Ultimate 32-bit

 

The Generic MLC SSD Problem in the Real World Overall System Performance with SYSMark 2007
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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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