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
Hey, There’s an Elephant in the Room
When the first X25-M reviews went live a few people discovered something very important, something many of us (myself included) missed and should’ve addressed: the drive got slower the more you filled it up. It’s no great mystery why this happened, but it seemed odd at the time because it went against conventional thinking.
LegitReviews was one of the first to spot the SSD slowdown phenomenon, good work Nate.
It’s worth mentioning that hard drives suffer from the same problem; just for a different reason.
Hard drives store data on platters; the platters rotate while an arm with read/write heads on it hovers over the surface of the platter and reads data while the platter spins. The diameter of the platter is greater the further out on the platter you go, that’s just how circles work. The side effect is that for the same amount of rotation, the heads can cover more area on the outside of the platter than on the inside.
The result is that transfer speeds are greater on the outer sectors of the platter than on the inner ones. OSes thus try to write as much data to the outer sectors as possible, but like beachfront property - there’s only a limited amount of space. Eventually you have to write to the slower parts of the drive and thus the more full your drive is, the slower your transfer rates will be for data stored in the innermost sectors.
Fragmentation also hurts hard drive performance. While modern day hard drives have gotten pretty quick at transferring large amounts of data stored sequentially, spread the data out all around the platter and things get real slow, real fast.
Randomness is the enemy of rotational storage.
Solid state drives aren’t supposed to have these issues. Data is stored in flash, so it doesn’t matter where it’s located, you get to it at the same speed. SSDs have +5 armor immunity to random access latency (that’s got to be the single most geeky-sounding thing I’ve ever written, and I use words like latency a lot).
So why is it that when you fill up a SSD like Intel’s X25-M that its performance goes down? Even more worrisome, why is it that when you delete data from the drive that its performance doesn’t go back up?
While SSDs are truly immune to the same problems that plague HDDs, they do also get slower over time. How can both be true? It’s time for another lesson in flash.
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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!