The SSD Anthology: Understanding SSDs and New Drives from OCZ
by Anand Lal Shimpi on March 18, 2009 12:00 AM EST- Posted in
- Storage
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.
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Hrel - Thursday, April 9, 2009 - link
although, I have some issues which I have put in an e-mail sent to Anand; can't wait for you response.Hrel - Thursday, April 9, 2009 - link
Instead of making me dinner can you send me that test system instead??? Please!!!Hrel - Thursday, April 9, 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.sfisher64 - Wednesday, April 8, 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?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.marraco - Tuesday, April 7, 2009 - link
This article is popular :)BLHealthy4life - Monday, April 6, 2009 - link
Intel 9.1.1.1010 (Intel) Where are these drivers? I can only find version 1007 and not 1010....Thanks
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
irondukes - Friday, April 3, 2009 - link
Hi-- Do SLCs suffer from performance degradation, or are the controllers pretty agressive at erasing the data since they have far longer read-write cycles? Please help! Deciding between an X25E and X25Mmdavies - Friday, April 3, 2009 - link
I'm reading this about a day late - got my Patriot PE256GS25SSDR 2.5" 256GB yesterday since I'm bad about destroying hard drives. this drive, in a word, was excruciating. I'll be replacing it with one of your recommended drives today.Thanks