Free Space to the Rescue

There’s not much we can do about the scenario I just described; you can’t erase individual pages, that’s the reality of NAND-flash. There are some things we can do to make it better though.

The most frequently used approach is to under provision the drive. Let’s say we only shipped our drive with 20KB of space to the end user, but we actually had 24KB of flash on the drive. The remaining 4KB could be used by our controller; how, you say?

In the scenario from the last page we had to write 12KB of data to our drive, but we only had 8KB in free pages and a 4KB invalid page. In order to write the 12KB we had to perform a read-modify-write which took over twice as long as a 12KB write should take.

If we had an extra 4KB of space our 12KB write from earlier could’ve proceeded without a problem. Take a look at how it would’ve worked:

We’d write 8KB to the user-facing flash, and then the remaining 4KB would get written to the overflow flash. Our write speed would still be 12KB/s and everything would be right in the world.

Now if we deleted and tried to write 4KB of data however, we’d run into the same problem again. We’re simply delaying the inevitable by shipping our drive with an extra 4KB of space.

The more spare-area we ship with, the longer our performance will remain at its peak level. But again, you have to pay the piper at some point.

Intel ships its X25-M with 7.5 - 8% more area than is actually reported to the OS. The more expensive enterprise version ships with the same amount of flash, but even more spare area. Random writes all over the drive are more likely in a server environment so Intel keeps more of the flash on the X25-E as spare area. You’re able to do this yourself if you own an X25-M; simply perform a secure erase and immediately partition the drive smaller than its actual capacity. The controller will use the unpartitioned space as spare area.

Understanding the SSD Performance Degradation Problem The Trim Command: Coming Soon to a Drive Near You
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  • Gasaraki88 - Friday, March 20, 2009 - link

    RAID is a universal standard so if you take two RAID0 drives out and move them to another computer with a RAID controller, it SHOULD just work if the original RAID was doing it correctly. Reply
  • coil222 - Wednesday, March 18, 2009 - link

    Yes I run a pair of MTRON 7500s in a raid 0 stripe for my OS and Gaming (wow). I don't recall numbers off the top of my head but tests were better on the raid 0 than a single drive configuration.

    Watch this:
    http://www.youtube.com/watch?v=96dWOEa4Djs&fea...">http://www.youtube.com/watch?v=96dWOEa4Djs&fea...
    Reply
  • sawyeriii - Wednesday, March 18, 2009 - link

    I just wanted to state how much I loved the combination of technical and real world information in this article.

    What is the possibility of having different page sizes built into a drive? I.e. you could have a drive with many 1k page packages on one die, 2k on another, and most others 4k. Could that theoretically help? Could the controllers work with that (or would you need to combine multiple 1k's into a 4k transfer size)?

    PS One note on page 3, the VelociRaptor and Intel in the first chart (responce time) are switched, however the text is correct.
    Reply
  • StormyParis - Wednesday, March 18, 2009 - link

    the ugly truth is that an SSD won't let you do anything that you couldn't do without it, and due to its cost and small capacity, it's not a replacement drive, it's an extra drive: not less power consumption but more, not less noise but just the same. You just gain a bit of time when booting up and lauching apps... which I do about 1/week and 1/day, respectively. Assuming your system has enough RAM (and if it doesn't, buy RAM before buying an SSD !), you won't feel much difference once the apps are launched.

    For the same cost, I'd rather buy a bigger screen.

    It's urgent to wait for prices to come down. But I'm all for lots of people buying them now and help get the price down for us wiser buyers.
    Reply
  • Rasterman - Thursday, March 19, 2009 - link

    I've already decided my next system in a few months will have one, after you go through 5 hard drive failures (over several years) lets see how much your willing to pay to not have to put up with it anymore. If you use your PC for anything useful (work) then an SSD is a no brainer even at $1000/64GB IMO if the data security is there, speed is secondary for me.

    When you already have the best screen, video card, memory, why not have the best drive? And your argument is pretty dumb, almost any upgrade won't let you do anything that you couldn't do without it, not just SSDs.
    Reply
  • Calin - Wednesday, March 18, 2009 - link

    You get lower power due to the lower power use of the SSD and the fact that the other drive is not stressed with difficult access patterns (small random reads/writes). Remember that idle power of a SSD drive is very low Reply
  • 7Enigma - Wednesday, March 18, 2009 - link

    No, his comment was accurate for most users. Due to the small capacities and high cost these will be used as boot drives primarily with maybe a single heavily used program (say the current game or program you are playing/using), the rest will be on an additional drive. So while the power consumption of the SSD would be less than the old drive, the aggregate power usage of both (even when the larger storage drive is primarily at idle) will be higher than the single HD.

    And I believe you meant to say traditional HD for idle power?
    Reply
  • strikeback03 - Wednesday, March 18, 2009 - link

    If all you were going to throw on the drive is the OS and a game, a 32GB drive should be plenty. The reason the 80GB and up range is important is so general consumers can load all their programs on it.

    But yes, in consumer usage other than a laptop, some people who were previously using one drive for both boot and storage would likely need a mechanical HDD is addition to the SSD. OTOH, those who were using a Velociraptor (or RAID array) for boot and another drive for storage will see their power consumption decrease.
    Reply
  • sawyeriii - Wednesday, March 18, 2009 - link

    Have you used a SSD? (If so which)

    I would state that it is not a luxary product, it is a premium product. The price difference you pay WILL translate to faster performance (if you choose correctly). More RAM only helps upto a point.

    Remember performance is based on a system of parts...
    CPU
    RAM
    NORTHBRIDGE
    GPU
    SOUTHBRIDGE
    I/O INTERFACE
    HDD/SDD

    Microsoft's Windows Experience Index has specific flaws, but the concept is sound... The system can only go a fast as the slowest component in the system (relative to the amount of time used by that component).
    Reply
  • Testtest - Wednesday, March 18, 2009 - link

    ... there's also Supertalent's Ultradrive ME (MLC) and LE (SLC) and Photofast's G-Monster v3

    At least the Supertalent drives are quite a bit cheaper with the same drive layout/controller than the Vertex drives and only differ in the firmware (which isn't bad either).

    It's however possible at least with the Ultradrive ME currently to provoke a kinda timeout error after they've been fully filled once and then still beeing written on. I don't own a Vertex so I can't test that there but if it was a controller issue, it should pop up there sooner or later as well (if you take a look in their suppport forum some error reports seem very similar).

    Intels have their 80% bug, Indilinx drives have their issues too it seems - let's hope that firmware can cure it!

    Great article btw!
    Reply

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