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
POST A COMMENT

273 Comments

View All Comments

  • KadensDad - Tuesday, October 27, 2009 - link

    How do these drives fail? I have heard that they will just suddenly die, no more writes or reads possible. What I would like to know is what happens when it dies? Do you lose all data? Just can't write anymore? How does the OS respond? Any early warnings? What about e.g. CRC? How does possibility of data corruption compare to traditional SSD? What about RAID? Since the drives are electrical, not mechanical, this reduces the number of failure vectors and environmental concerns (e.g., ambient temperature over lifetime of the drive). Won't SSDs therefore fail closer together in time in a RAID configuration? This reduces the window of opportunity for fixing an array and also decreases the applicability of RAID, however marginal.
    Reply
  • Dewend - Friday, March 04, 2016 - link

    My partner and i also were seated for lunch, whenever i mentioned to her that I read a script each and every morning newspaper, therefore i chosen to do a little research. Thankfully, I stumbled upon this website, which helped me discover why people consider even thinking about this. http://followersteam.com Reply
  • Askipod - Thursday, November 17, 2016 - link

    This is cool! Your website is great Hey Your information is astounding!! I will recommend it to my brother and anybody that could be attracted to this topic. Reply
  • Askipod - Thursday, November 17, 2016 - link

    WOW. I am very glad to join this comunity and enjoy your article. Your article shared me so interesting information here, looking forward to your update. http://www.nasze.media.pl/pisanie-tekstow-jako-spo... Reply
  • Askipod - Thursday, November 17, 2016 - link

    It's actually a cool and useful piece of information. I am glad that you shared this helpful information with us. Please keep us informed like this. Thank you for sharing http://www.nasze.media.pl/porozmawiajmy-o-pieniadz... Reply
  • jackeyroe - Friday, April 22, 2016 - link

    Great, that what you said I agree and I think that all your opinion are nice and smart for me. If you want any sports shoes you can feel free to my website and I will share you coupon code. And for your this opinion of SSD might I know that is it possible for my website, if it is possible I will try to find is there any more tips that could improve all the functions of my sports shoes site. If it works then will be my pleasure and I will share the great article to all my kind friend, they will be happy to share it into the network of them. Would you please take a look to my website firstly:
    http://www.kicksvovo.com/
    Reply
  • davidsmith123 - Thursday, July 07, 2016 - link

    That sure was a lot to take in! Fantastic article though, it has really opened my eyes to the possibilities that Solid State Drives provide. Probably wont be buying one in the immediate future given the so-called depression and such things, but i will certainly keep up with SSD progress.
    Thanks again for your fantastic articles - im sure im not the only one who really appreciates them :)
    http://www.hubnames.com/
    Reply
  • devdeepc - Friday, September 02, 2016 - link

    What about e.g. CRC? How does possibility of data corruption compare to traditional SSD? What about RAID? Since the drives are electrical, not mechanical, this reduces the number of failure vectors and environmental concerns Reply
  • Rahul Ji - Sunday, August 21, 2016 - link

    Dear KadensDad, these drivers fail all the time. With the new technology and new softwares coming , everyday some drivers and some softwares go outdated. This ought to happen. But, what will not go outdated is our Microsoft xbox live codes at http://xbcodejunction.com . These codes work anywhere anytime, anybody can use them. Just so easy to get and use. So come and try your copy for free. Reply
  • adsmith82 - Monday, September 14, 2009 - link

    I need to run HDDErase on an X25-M. No matter what bootable CD or flash drive I create, HDDErase does not see either of my SATA hard drives. I already disabled AHCI in BIOS. Also, I am using version 3.3. I know that 4.0 does not work with the X25-M.

    Can someone help me troubleshoot this please? Thanks.
    Reply

Log in

Don't have an account? Sign up now