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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  • Mocib - Thursday, October 09, 2008 - link

    Good stuff, but why isn't anyone talking about ioXtreme, the PCI-E SSD drive from Fusion-IO? It baffles me just how little talk there is about ioXtreme, and the ioDrive solution in general. Reply
  • Shadowmaster625 - Thursday, October 09, 2008 - link

    I think the Fusion-IO is great as a concept. But what we really need is for Intel and/or AMD to start thinking intelligently about SSDs.

    AMD and Intel need to agree on a standard for an integrated SSD controller. And then create a new open standard for a Flash SSD DIMM socket.

    Then I could buy a 32 or 64 GB SSD DIMM and plug it into a socket next to my RAM, and have a SUPER-FAST hard drive. Imagine a SSD DIMM that costs $50 and puts out even better numbers than the Fusion-IO! With economy of scale, it would only cost a few dollers per CPU and a few dollars more for the motherboard. But the performance would shatter the current paradigm.

    The cost of the DIMMs would be low because there would be no expensive controller on the module, like there is now with flash SSDs. And that is how it should be! There is NO need for a controller on a memory module! How we ended up taking this convoluted route baffles me. It is a fatally flawed design that is always going to be bottlenecked by the SATA interface, no matter how fast it is. The SSD MUST have a direct link to the CPU in order to unleash its true performance potential.

    This would increase performance so much that if VIA did this with their Nano CPU, they would have an end product that outperforms even Nehalem in real-world everyday PC usage. If you dont believe me, you need to check out the Fusion-IO. With SSD controller integration, you can have Fusion-IO level performance for dirt cheap.

    If you understand what I am talking about here, and can see that this is truly the way to go with SSDs, then you need to help get the word to AMD and Intel. Whoever does it first is going to make a killing. I'd prefer it to be AMD at this point but it just needs to get done.
    Reply
  • ProDigit - Tuesday, October 07, 2008 - link

    Concerning the Vista boottime,I think it'd make more sense to express that in seconds rather than MB/s.
    I rather have a Windows boot in 38seconds article,than a windows boots with 51MB/s speeds.. That'd be totally useless to me.

    Also, I had hoped for entry level SSD cards, replacements for mininotebooks rather in the category of sub 150$ drives.
    On an XP machine, 32GB is more then enough for a mininotebook (8GB has been done before). Mininotebooks cost about $500,and cheap ones below $300. I,as many out there, am not willing to spend $500 on a SSD drive, when the machine costs the same or less.

    I had hoped maybe a slightly lower performance 40GB SSD drive could be sold for 149$,which is the max price for SSD cards for mini notebooks.
    for laptops and normal notebooks drives upto 200-250$ range would be enough for 64-80GB. I don't agree on the '300-400' region being good for SSD drives. Prices are still waaay too high!
    Ofcourse we're paying a lot of R&D right now,prices should drop 1 year from now. Notebooks with XP should do with drives starting from 64GB,mini notebooks with drives from 32-40GB,and for desktops 160GB is more than enough. In fact, desktops usually have multiple harddrives, and an SSD is only good for netbooks for it's faster speeds, and lower powerconsumption.
    If you want to benefit from speeds on a desktop,a 60-80GB will more then do, since only the Windows, office applications, anti-virus and personal programs like coreldraw, photoshop, or games need to be on the SSD drive.
    Downloaded things, movies, mp3 files, all those things that take up space might as well be saved on an external/internal second HD.

    Besides if you can handle the slightly higher game loadtimes on conventional HD's, many older games already run fine (over 30fps) on full detail, 1900x??? resolution.
    Installing older games on an SSD doesn't really benefit anyone, apart from the slightly lower loadtimes.

    Seeing that I'd say for the server market highest speed and largest diskspace-size matter, and occasionally also lowest power consumption matter.
    => highest priced SSD's. X >$1000, X >164GB /SSD

    For the desktop high to highest speed matters, less focus on diskspace size and power consumption.
    => normal priced SSD's $250 > X > $599 X > 80GB/SSD

    For the notebooks high speed and lowest power consumption matter, smaller size as compensation for price.
    => Normal priced SSD's $175 > X > $399 X > 60GB/SSD

    For the mininotebook normal speed, and more focus on lower power consumption and lowest pricing matter!
    => Low powered small SSD's $75 > X > $199 X > 32GB/SSD
    Reply
  • gemsurf - Sunday, October 05, 2008 - link

    Just in case anyone hasn't noticed, these are showing up for sale all over the net in the $625 to $750 range. Using live search, I bought one from teckwave on ebay yesterday for $481.80 after the live search cashback from microsoft.

    BTW, Does Jmicron do anything right? Seems I had AHCI/Raid issues on the 965 series Intel chipsets a few years back with jmicron controllers too!
    Reply
  • Shadowmaster625 - Wednesday, September 24, 2008 - link

    Obviously Intel has greater resources than you guys. No doubt they threw a large number of bodies into write optimizations.

    But it isnt too hard to figure out what they did. I'm assuming that when the controller is free from reads or writes, that is when it takes the time to actually go and erase a block. The controller probably adds up all the pages that are flagged for erasure, and when it has enough to fill an entire block, then it goes and erases and writes that block.

    Assuming 4KB pages and 512KB blocks (~150,000 blocks per 80GB device) what Intel must be doing is just writing each page wherever they could shove it. And erasing one block while writing to all those other blocks. (With that many blocks you could do a lot of writing without ever having to wait for one to erase.) And I would go ahead and have the controller acknowledge the data was written once it is all in the buffer. That would free up the drive as far as Windows is concerned.

    If I was designing one of these devices, I would definately demand as much SRAM as possible. I dont buy that line of bull about Intel not using the SRAM for temporary data storage. That makes no sense. You can take steps to ensure the data is protected, but making use of SRAM is key to greater performance in the future. That is what allows you to put off erasing and writing blocks until the drive is idle. Even a SRAM storage time limit of just one second would add a lot of performance, and the risk of data loss would be negligable.

    Reply
  • Shadowmaster625 - Wednesday, September 24, 2008 - link

    OCZ OCZSSD2-1S32G

    32GB SLC, currently $395

    The 64GB version is more expensive than the Intel right now, but with the money they've already raked in who really thinks they wont be able to match intel performance or pricewise? Of course they will. So how can this possibly be that great of a thing? So its a few extra GB. Gimme a break, I would rather take the 32GB and simply juggle around stuff onto my media drive every now and then. Did you know you can simply copy your entire folder from the Program Files directory over to your other drive and then put it back when you want to use it? I do that with games all the time. It takes all of 2 minutes... Why pay hundreds of dollars extra to avoid having to do that? It's just a background task anyway. That's how 32GB has been enough space for my system drive for a long time now. (Well, that and not using Vista.) At any rate this is hardly a game changer. The other MLC vendors will address the latency issue.
    Reply
  • cfp - Tuesday, September 16, 2008 - link

    Have you seen any UK/Euro shops with these available (for preorder even?) yet? There are many results on the US Froogle (though none of them seem to have stock or availability dates) but still none on the UK one. Reply
  • Per Hansson - Friday, September 12, 2008 - link

    What about the Mtron SSD's
    You said they used a different controller vs Samsung in the beginning of the article but you never benchmarked them?
    Reply
  • 7Enigma - Friday, September 19, 2008 - link

    I would like to know the question to this as well... Reply
  • NeoZGeo - Thursday, September 11, 2008 - link

    The whole review is based on Intel vs OCZ Core. We all know OCZ core had issues that you have mentioned. However, what I would like to see is other drives test bench against OCZ core drive, or even the core II drive. Suppose the controller has a different firmware according to some guys from OCZ on the core 2, and I find that a bit bias if you are using a different spec item to represent all the other drives in the market. Reply

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