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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siberx - Thursday, March 19, 2009 - link
This is, very likely, the best article I have ever read, period. Online, in magazines, about any subject... this was an absolutely fantastic read. Suddenly, all smoke surrounding SSDs has cleared and the truth shines through in editorial brilliance. It's great to see that at least some computer news sites out there can still cut through the crap and get to the heart of the issue. My already high opinion of AnandTech has risen even further.Thank you for taking the immense time it must have taken to compile and assemble all this information - this article is now a must-read for *anybody* considering purchasing an SSD, and it's just about all the background you could need in one place.
In addition to all the extremely useful general SSD information contained within, the detailing of the issues with the JMicron controllers as well as OCZ's efforts to address the concerns to produce the best product possible (despite the reduced marketability to the uninformed) is reassuring and comforting in a world where tech companies seem more concerned with how much they can deceive their customers instead of producing quality products.
In short, the article is a win on all fronts, thank you greatly for posting it. When I purchase my first SSD (which I'm considering doing reasonably soon) this article, its information and suggestions, and OCZs actions to resolve the issues with its drives will definitely be at the forefront of my mind.
jkua - Thursday, March 19, 2009 - link
I have to say, I really appreciate the effort and throughness with which you have covered the state of the SSD market today. As an engineer and scientist, I applaud your methods in tracking down and reporting the major issues with SSDs. As a consumer, I really appreciate the timeliness of this article as I was just thinking of putting an SSD in a netbook for a robotics application where mechanical drives are not ideal.Cheers!
jkua - Thursday, March 19, 2009 - link
That said, one thing I would have like to have seen is some numbers on power consumption for these drives compared to average mechanical desktop and laptop drives.aamsel - Thursday, March 19, 2009 - link
Anyone have a link to the Intel HDD ERASE program that Anand referred to?HolyFire - Thursday, March 19, 2009 - link
http://www.ultimatebootcd.com/download.html">http://www.ultimatebootcd.com/download.html (includes HDD erase 3.1)http://cmrr.ucsd.edu/people/Hughes/SecureErase.sht...">http://cmrr.ucsd.edu/people/Hughes/SecureErase.sht... (version 4.0)
AnnonymousCoward - Thursday, March 19, 2009 - link
AWESOME ARTICLE.The huge difference in read/write flash performance looks a lot like this article: http://www.anandtech.com/memory/showdoc.aspx?i=257...">http://www.anandtech.com/memory/showdoc.aspx?i=257...
wind glider - Thursday, March 19, 2009 - link
Thanks for the orgasmic review.wicko - Wednesday, March 18, 2009 - link
Had a really good read here, thanks for the history and info, Anand. The only thing I don't understand is what the importance of random write is? What kind of task would benefit from high random write speeds (maybe copying many files at once)? I'm tempted to pick up a vertex drive but it depends on whether or not random write will be important for me. But the price... whoa, pretty damn expensive here in Canada.. http://www.ncix.com/products/index.php?sku=36023&a...">http://www.ncix.com/products/index.php?...X120G&am... - $625 for a 120GB!!! I kind of want 2, for RAID0, I have a lot of games installed (steam folder alone is 100GB lol). Might even have to raid 3 of em.. but not for $1800 lol.strikeback03 - Thursday, March 19, 2009 - link
As mentioned in the article, the OS in general makes lots of random writes. Send an IM, it writes to a log. Load a website, it caches some images.AnnonymousCoward - Thursday, March 19, 2009 - link
>I'm tempted to pick up a vertex drive but it depends on>whether or not random write will be important for me.
Keep in mind, its random write is twice as fast as mechanical HDs.
>But the price...
It's only $110USD/32GB.