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.
Facebook
Twitter
RSS
250 Comments
View All Comments
sbuckler - Wednesday, March 18, 2009 - link
Depends on how smart the controller is? Shuffling around the data now and again in the background would make sense.Frallan - Wednesday, March 18, 2009 - link
@AT
This is why i come to AT to read up on the developments.
@OCZ
Well played :0)
The ruler of the roost are the Intels however I will be able to afford one of those when there are cows enjoying themselfs by dancing on the moon. My next upgrade will be a Vertex - not only bc its Valu for money but equally much bc. OCZ obviously takes care of thier customers and listens to reason.
pmonti80 - Wednesday, March 18, 2009 - link
This is the kind of article that makes me come back here.nowayout99 - Wednesday, March 18, 2009 - link
OCZ, you should listen to Uncle Anand. ;) Hopefully Mr. Petersen understands that it's tough love.And the final product seems perfectly cool -- great performance at a better price than Intel. It's the first SSD I'd be able to reasonably consider.
SOLIDNecro - Wednesday, March 18, 2009 - link
Thx for this article Anand, I have been in a hotly contested debate over OCZ vs Samsung with my "Asperger Enhanced" nemisis/close friend...(In all fairness, I should mention I use the BiPolar SSE instruction set myself)
He was only looking at Samsung, I said he should look into what OCZ has now.
His reply was "I don't know them, and don't want to be disapointed"
(Long story behind that...He's from the Server/Workstain/HPC crowd, I am from the hardcore OC/Gamer/Desktop group, so he is not familiar with OCZ)
Looks like the Samsung (And alot of others) has "Issues" with performance degrading over time that are somewhat solved by Intel and OCZ (Plus maybe a few other companies that use the Rev B JMicron controller on there low cost SSD's)
I agree the OCZ Vertex offers the best bang for low buck SSD today, and I am tempted to grab one. But a year from now, anyone that bought a current gen MLC SSD will be saying "I coulda had a V-8" if that TRIM technology does what it promises!!!
James5mith - Wednesday, March 18, 2009 - link
As people continue to try and push the envelope of storage performance in a variety of ways, and as 6gbps SATA becomes available, the performance of SSD's will only go up.As always, I wanted to say thanks for the great article and keep them coming. It's the only way the rest of us can keep pace with what's happening out there in the world of performance storage.
vailr - Wednesday, March 18, 2009 - link
Is there any benefit in using 2 SSD's in a Raid 0 configuration?And: any differences between motherboard Intel Raid vs. a Raid controller card from Areca, for example. Also: can the "Trim" command work while in Raid mode? Probably not, I'm guessing...
7Enigma - Thursday, March 19, 2009 - link
Raid0 is really the holy grail for SSD's. The low risk of failure of SSD's which normally makes Raid0 with typical mechanical HD's more dangerous is very appealing. My personal storage-size goal is ~120-160gigs. Once they reach that size for under $300 I think I'm going to jump in. But I'm more likely to grab 2 60's or 2 80's and Raid0 them than get a single large SSD. The added performance will outweigh the higher power draw of 2 drives, and should make them extremely competitive with Intel's offerings (or whatever holds the crown at the time).I figure it will be about a year or so until the prices are in that range, as 2 60gig Vertex drives will currently run you about $400 after rebate.
I can't wait to jump on that upgrade and will then put my current 250gig mechanical drive as the storage drive (I don't use a ton of space in general as I have a 320gig external backup).
Rasterman - Thursday, March 19, 2009 - link
The problem with doing that is if you want to move your drives to another system they won't work, so upgrading is a pain. You could image them I guess, but plugging one drive in is much simpler. I had an older XP install that made it through 3-4 different systems.I would also question real world results, if you're going at 250MB/s or 500MB/s its not even going to be noticeable unless you are doing some massive video editing or some other huge file operations, and as Anand says, SSDs don't fill this role right now as they are super expensive per GB. So if you really are editing video a lot, you are going to need a hell of a lot more space than SSDs can offer you.
Gasaraki88 - Friday, March 20, 2009 - link
RAID is a universal standard so if you take two RAID0 drives out and move them to another computer with a RAID controller, it SHOULD just work if the original RAID was doing it correctly.