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

273 Comments

View All Comments

  • brandensilva - Friday, April 10, 2009 - link

    Great article! I respect that OCZ made the necessary changes to make this drive work. I'd rather take a slightly slower drive if it meant consistent performance.

    If my hard drive started to stutter I'd flip out! I'm glad that they took the feedback and instead of selling faulty drives, that would ultimately hurt their brand, they decided to go back to the drawing board and iron out the kinks. I'm not expecting them to compare to Intel's 25-M per price or performance. They don't have nearly the cash or manufacturing capacity to compete with Intel but they do have that small business feel with receiving feedback and making improvements, which is important to customers.

    Lets hope they continue to utilize that aspect of their business and further improve on their products and bring us some reliable SSD's in the future.
    Reply
  • Hrel - Thursday, April 09, 2009 - link

    although, I have some issues which I have put in an e-mail sent to Anand; can't wait for you response. Reply
  • Hrel - Thursday, April 09, 2009 - link

    Instead of making me dinner can you send me that test system instead??? Please!!! Reply
  • Hrel - Thursday, April 09, 2009 - link

    I was wondering what controller the OCZ solid Series is based on??? Will I experience hiccups with that drive or not? Is the point of my question. Reply
  • sfisher64 - Wednesday, April 08, 2009 - link

    I just purchased a Dell Latitude E6400 with a 64GB Ultra Performance Solid State Drive. Does anyone know what type of drive this is, and where it fits in the spectrum described in this article? Reply
  • Baffo - Saturday, April 11, 2009 - link

    The Dells use the Samsung drives (you should see this on the bottom if you pull it out). However, as much as I wish this was one of the newer controllers (I have a few of these at work as well), the testing cycles demanded by Dell probably mean these are the older controllers. Reply
  • marraco - Tuesday, April 07, 2009 - link

    This article is popular :) Reply
  • jesusclay - Monday, November 14, 2016 - link

    All issues related to SSD are indeed important, since the storage of all current computers opts (when possible) for the SSD. Here I use this technology, which allows a much faster speed than HD discs and which are very slow compared to the first , no doubt.
    My site: https://www.geradordecpfvalido.com

    Thanks and the post is very clear.
    Reply
  • BLHealthy4life - Monday, April 06, 2009 - link

    Intel 9.1.1.1010 (Intel) Where are these drivers? I can only find version 1007 and not 1010....

    Thanks
    Reply
  • BLHealthy4life - Sunday, April 12, 2009 - link

    found it....

    Intel obviously keeps the X58 chipset drivers current for their own boards, just not other mfgs boards....

    They installed fine on my R2E..

    BL
    Reply

Log in

Don't have an account? Sign up now