The Blind SSD

Modern OSes talk to hard drives using logical block addressing. While hard drives are rotational media, logical block addressing organizes sectors on a hard drive linearly. When you go to save a file, Windows simply issues a write command for your file at a specific logical block address, say LBA 15 for example.

Your OS knows what LBAs are available and which ones are occupied. When you delete a file, the LBAs that point to that file on your hard disk are listed as available. The data you’ve deleted hasn’t actually been removed and it doesn’t get wiped until those sectors on the drive are actually overwritten.

Believe it or not, SSDs actually work the same way.

The flash translation layer in a SSD controller maps LBAs to pages on the drive. The table below explains what happens to the data on the SSD depending on the action in the OS:

Action in the OS Reaction on a HDD Reaction on an SSD
File Create Write to a Sector Write to a Page
File Overwrite Write new data to the same Sector Write to a Different Page if possible, else Erase Block and Write to the Same Page
File Delete Nothing Nothing

 

When you delete a file in your OS, there is no reaction from either a hard drive or SSD. It isn’t until you overwrite the sector (on a hard drive) or page (on a SSD) that you actually lose the data. File recovery programs use this property to their advantage and that’s how they help you recover deleted files.

The key distinction between HDDs and SSDs however is what happens when you overwrite a file. While a HDD can simply write the new data to the same sector, a SSD will allocate a new (or previously used) page for the overwritten data. The page that contains the now invalid data will simply be marked as invalid and at some point it’ll get erased.

Strength in Numbers, What makes SSDs Fast Understanding the SSD Performance Degradation Problem
POST A COMMENT

312 Comments

View All Comments

  • seotab - Wednesday, January 11, 2017 - link

    You may already get enough reasons about why you should download showbox on your device. get it using https://showboxdownload.site 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
  • hapeid - Wednesday, January 25, 2017 - link

    Hy Anand.

    I wanted to compliment you on what I think was an excellent article. This is the type of thing I really have always liked from Anandtech. The detailed background, the technical reasons for the issues and then a thorough review of the current state of things.

    I just finished upgrading my desktop. The only remaining item I wanted to replace was the hard disk. I had been thinking about getting a Velociraptor but instead I just ordered a 60GB Vertex from Newegg.
    Thank you.
    Reply
  • DHIAN - Friday, January 06, 2017 - link

    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.servicekomputerbali.com/ 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
  • giyan - Friday, January 06, 2017 - link

    This is good for car tool ,and also needs software http://www.forobd.de/.i think it is helpful for me! Reply
  • giyan - Friday, January 06, 2017 - link

    this is right . http://www.forobd.de/ Reply
  • MAKK2016 - Friday, December 30, 2016 - 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.

    SImon : http://www.e-consulting.ma/
    Reply

Log in

Don't have an account? Sign up now