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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  • Abjuk - Wednesday, September 02, 2009 - link

    Agreed CM, my current project at work takes about six minutes to build from scratch and CPU usage never gets above about 35%. The process is totally IO bound.

    It really depends on whether you have several large source files or several hundred small ones.
    Reply
  • Weyzer - Tuesday, September 01, 2009 - link

    Good article and testing, but why was the Crucial M225 not mentioned at all? It's performance is similar to the vertex drives, I know, but I think it could have been mentioned somewhere, if it is in the good or bad range. Reply
  • jasperjones - Tuesday, September 01, 2009 - link

    javascript:link('frmText') $997 @ Newegg omgomgomg

    Needless to say, that price will come down quickly. So more seriously, after reading the article I really feel I understand better what to look for in an SSD. Thanks!
    Reply
  • paesan - Tuesday, September 01, 2009 - link

    Wow, does NE really think that anyone will buy the Intel drive at that price. OMG!!! Funny thing, it is in stock and it says limit 1 per customer. Lol Reply
  • CList - Tuesday, September 01, 2009 - link

    Obviously someone is buying them at that price or they'd lower it. The people who can't wait two or three weeks and are willing to be gouged for these drives are the ones that allow NewEgg to give us low margins on other products while not going out of business :D

    Reply
  • ravaneli - Tuesday, September 01, 2009 - link

    I just decided to buy one and when I opened newegg i couldn't believe my eyes. I hope that is only because they have a few drives left, and once Intel pumps up some stock in the retailers the prices will go back to Intel's retail.

    Does anyone know what are the production capabilities of Intel's SSD factories? I don't want to wait a whole year until the market saturates.
    Reply
  • LazierSaid - Tuesday, September 01, 2009 - link

    This article was so good that Newegg doubled their X25M G2 prices overnight.

    Reply
  • medi01 - Tuesday, September 01, 2009 - link

    Yep, very impressive advertisement indeed. Reply
  • HVAC - Tuesday, September 01, 2009 - link

    I'd rather have ewoks in the sequels than Jar-jar ... Reply
  • Naccah - Tuesday, September 01, 2009 - link

    Newegg's prices on all the Intel SSDs skyrocketed. The X-25 G2s are $499 now. Is this price a reflection of the high demand or did Intel change the price again? Reply

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