Understanding Spare Area (or Why My 80GB Drive Appears as 74.5GB)

Intel's 80GB X25-M has 80GB of NAND flash on it. That's 85,899,345,920 bytes or 80 x 1024^3 bytes (1024 bytes in a kilobyte x 1024 kilobytes in a megabyte x 1024 megabytes in a gigabyte x 80 gigabytes).

Hard drive makers however assume that 80GB means 80,000,000,000 bytes, since they use the definition of 1GB = 1,000,000,000 bytes. SSD vendors thus use the same definition. Now 80,000,000,000 bytes actually equals 74.5GB, so that's all the space you get to use on the drive.

How much space is there really on the drive? 80GB. How much space does Windows let you use? 74.5GB. What happens to the remaining 5.5GB? It's used by the drive's controller as spare area.

Intel’s controller is dynamic, it uses the entire drive as spare area until you’ve written every LBA once. Then it relies on the remaining 7.5% of non-user-space as its scratch pad. That’s why its new, out of box, performance is so good.

Other controllers may not be quite as dynamic, but they may also take a smaller performance hit when fully used. Why would Intel work so hard to make its out of box performance so high, even when it’ll be short lived? Because of TRIM.

A Wear Leveling Refresher: How Long Will My SSD Last? The Instruction That Changes (almost) Everything: TRIM
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  • jengeek - Wednesday, September 02, 2009 - link

    As of 09-02-09 from Toshiba Direct:

    80GB = $243
    160GB = $473

    http://www.toshibadirect.com/td/b2c/adet.to?poid=4...">http://www.toshibadirect.com/td/b2c/adet.to?poid=4...

    http://www.toshibadirect.com/td/b2c/adet.to?poid=4...">http://www.toshibadirect.com/td/b2c/adet.to?poid=4...
    Reply
  • gfody - Thursday, September 03, 2009 - link

    nice thank you, ordered mine from here
    screw Newegg! :D
    Reply
  • jengeek - Wednesday, September 02, 2009 - link

    Both are G2, in stock and ship the next day

    Both are retail box including the installation kit

    Best price I've found
    Reply
  • ARoyalF - Sunday, September 13, 2009 - link

    Thank you posting that!

    I was going to wait out that awful price hike over at the egg.

    You rock
    Reply
  • ElderTech - Tuesday, September 01, 2009 - link

    It's difficult to imagine the amount of time and effort that went into this article, Anand. Just the clean installs of Win7 took a fair amount of extra effort, let alone the other detailed diagrams and testing involved. From an old technology advocate over many years of working to keep pace with Moore's Law in a variety of research environments, your site provides the most satisfying learning experience of all. A sincere thank you!

    PS: As for the availability of the G2, it pops in and out of stock at a variety of online retailers, including Newegg, of course, as well as MWave. Both had it available for a short while at $249, Newegg on Friday and MWave today, Monday. However, it's out of stock presently as of midnight, EST 9-1-09 at both, with MWave still at $249 but Newegg going from there to $279 over the weekend and now at an amazing $499! OUCH. Sounds like supply and demand gouging if the price holds when they are next available! There is also some stock available in the distributor channel from small Intel Partners, as I confirmed by calling around the Chicago area. You might give this a try tomorrow. Good luck!
    Reply
  • blyndy - Monday, August 31, 2009 - link

    You really got performance anxiety because some high-profile people/sites liked your article and linked to it? It's hardly like it got printed in some prestigious science journal and the publishers are waiting on a follow-up.

    It was just the first time that SDD operation had been detailed in plain english from a reputable website.

    Enough of this 'anthology' nonsense, I don't care if it's 1 page or 20, just tell me how some of the new SSDs perform (eg OCZ, Western Digital). You've already detailed how they work so now I want to know which ones do/will support TRIM and some details on the controller. Nothing to get anxious about.
    Reply
  • Anand Lal Shimpi - Monday, August 31, 2009 - link

    Indeed I did get performance anxiety after the last one, I even got it after the first X25-M. It's not so much the linkage, but the feedback from all of you guys. I received more positive feedback to the last SSD article than any one prior. More than anything I don't want to let you all down and I want to make sure I live up to everyone's expectations.

    As far as your interests go, all three manufacturers (Indilinx, Intel and Samsung) have confirmed support for TRIM. When? I'd say all three before December.

    Take care,
    Anand
    Reply
  • cacca - Thursday, September 03, 2009 - link

    Dear Anand i really thank you for your SSD articles, the improvements in this area seem tangible.
    Can I ask you to test Fusion-IO & ioXtreme, i am really curious to see how this other approach performs.
    I know that isn't a perfect apple to apple comparison but at least we could compare the per $ performance.

    Best regards

    Ca
    Reply
  • vol7ron - Monday, August 31, 2009 - link

    Good article.

    I have a follow-up question regarding your size suggestion.

    In more words you say, "get the size you need," but don't these drives perform that much better in a RAIDed system?

    The cost per GB isn't that much more if you're looking at getting a 160GB Intel drive, to get the 2x 80GB instead.

    SSDs are more reliable than HDs and you have the benefit of more RAM. 2x 32MB for an SSD in RAID0.


    Curious to hear your thoughts,
    vol7ron
    Reply
  • StraightPipe - Tuesday, September 01, 2009 - link

    Since RAID cards aren't going to support TRIM commands for a while, I'd stick with a large, single SSD.

    Anybody ahve any experience running these cards in RAID? I'd love to put some of these in my server, but i'm terrified of lossing data through the complexities of RAID combined with SSD.

    I'd love to do a simple RAID1 setup, but it looks like i may be better of waiting too.

    In the mean time, these look like a mean machine for an OS disk.
    Reply

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