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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GlItCh017 - Wednesday, March 18, 2009 - link
I just wanted to comment that the backstory portion to this article is simply the most interesting part to an article (or almost even an article inside the main article). On top of that, it is easily the most interesting article I have ever read simply because of that section. Really really must say that I enjoyed reading it!radguy - Wednesday, March 18, 2009 - link
I have been waiting for this one for a while and it was very informative. Thank you very much for it. I did pick up one of the patriot warp drives for my netbook. I was really happy until I installed avg free. So not running an antivirus on it anymore but I have drive image backup incase it goes bad. Overall pretty happy as it was only 80 bucks if I get my mir.I think I'm going to wait until windows 7 till I upgrade my primary desktop. 2 of those vertexs in raid 0 would be sweet though.
sleepeeg3 - Wednesday, March 18, 2009 - link
They were one of the first SSDs you reviewed and they use their own controller. How does their random write performance compare to everything else out now?These reviews made me totally reassess the purchase of the two Samsungs I bought. I had no idea the random writes on the Samsung drives were so bad. Other reviews show the Samsung drives doing better or at least near the X25-M in write tests: http://www.techreport.com/articles.x/15433/6">http://www.techreport.com/articles.x/15433/6 However, those tests probably would have been somewhat sequential.
nubie - Wednesday, March 18, 2009 - link
Grammatically awkward sentence on Page 21:"so if you own one of these drives - you owned a fixed version."
The tense is incorrect (own/owned). I think "own a fixed version" is still awkward, perhaps "you have the fixed version", also the "so" may be superfluous. You can replace the ", so if" with a "; if". Here is how I might re-write the sentence:
"The old firmware never shipped thanks to OCZ's quick acting; if you own one of these drives - you have a fixed version."
(I am not an expert, so feel free to correct me if I am wrong.)
Awesome article btw, thanks for setting me straight on SSD, I have been steering clear of them. I hope soon you can review SSD's and most are good to excellent. :)
Flyboy27 - Wednesday, March 18, 2009 - link
This article has answered every question I've had regarding SSDs recently. Thanks Anand!Flyboy27 - Wednesday, March 18, 2009 - link
If a 120gb Vertex was around $250 I would get one yesterday. I suppose I can wait though.7Enigma - Thursday, March 19, 2009 - link
For me, 2 60's or 2 80's for around that price and I'm sold. Want the Raid0.kgwagner - Wednesday, March 18, 2009 - link
I almost didn't read this article, as everybody and their brother seems to want to explain SSDs these days and most of the articles aren't much more than glorified press releases. But, this one truly took the drives to task and presented some valid information and explanations about the state of the art and where it needs to go. Kudos, Anand. Awesome show. Good job.Mr Perfect - Wednesday, March 18, 2009 - link
"Needless to say, there was some definite fallout from that review. I’m used to negative manufacturer response after a GPU review, but I’m always a bit surprised when it happens in any other segment."Obviously you can't make a business out of irritating manufacturers, but when there really are issues, the readers want to know about them. After all, that's why we come here!
gwolfman - Wednesday, March 18, 2009 - link
You own Anand. Keep up the good work. I've seen you cited from many sites about the work you've done, in particular with SSDs. Best article I've read in months!