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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coil222 - Wednesday, March 18, 2009 - link
Yes I run a pair of MTRON 7500s in a raid 0 stripe for my OS and Gaming (wow). I don't recall numbers off the top of my head but tests were better on the raid 0 than a single drive configuration.Watch this:
http://www.youtube.com/watch?v=96dWOEa4Djs&fea...">http://www.youtube.com/watch?v=96dWOEa4Djs&fea...
sawyeriii - Wednesday, March 18, 2009 - link
I just wanted to state how much I loved the combination of technical and real world information in this article.What is the possibility of having different page sizes built into a drive? I.e. you could have a drive with many 1k page packages on one die, 2k on another, and most others 4k. Could that theoretically help? Could the controllers work with that (or would you need to combine multiple 1k's into a 4k transfer size)?
PS One note on page 3, the VelociRaptor and Intel in the first chart (responce time) are switched, however the text is correct.
StormyParis - Wednesday, March 18, 2009 - link
the ugly truth is that an SSD won't let you do anything that you couldn't do without it, and due to its cost and small capacity, it's not a replacement drive, it's an extra drive: not less power consumption but more, not less noise but just the same. You just gain a bit of time when booting up and lauching apps... which I do about 1/week and 1/day, respectively. Assuming your system has enough RAM (and if it doesn't, buy RAM before buying an SSD !), you won't feel much difference once the apps are launched.For the same cost, I'd rather buy a bigger screen.
It's urgent to wait for prices to come down. But I'm all for lots of people buying them now and help get the price down for us wiser buyers.
Rasterman - Thursday, March 19, 2009 - link
I've already decided my next system in a few months will have one, after you go through 5 hard drive failures (over several years) lets see how much your willing to pay to not have to put up with it anymore. If you use your PC for anything useful (work) then an SSD is a no brainer even at $1000/64GB IMO if the data security is there, speed is secondary for me.When you already have the best screen, video card, memory, why not have the best drive? And your argument is pretty dumb, almost any upgrade won't let you do anything that you couldn't do without it, not just SSDs.
Calin - Wednesday, March 18, 2009 - link
You get lower power due to the lower power use of the SSD and the fact that the other drive is not stressed with difficult access patterns (small random reads/writes). Remember that idle power of a SSD drive is very low7Enigma - Wednesday, March 18, 2009 - link
No, his comment was accurate for most users. Due to the small capacities and high cost these will be used as boot drives primarily with maybe a single heavily used program (say the current game or program you are playing/using), the rest will be on an additional drive. So while the power consumption of the SSD would be less than the old drive, the aggregate power usage of both (even when the larger storage drive is primarily at idle) will be higher than the single HD.And I believe you meant to say traditional HD for idle power?
strikeback03 - Wednesday, March 18, 2009 - link
If all you were going to throw on the drive is the OS and a game, a 32GB drive should be plenty. The reason the 80GB and up range is important is so general consumers can load all their programs on it.But yes, in consumer usage other than a laptop, some people who were previously using one drive for both boot and storage would likely need a mechanical HDD is addition to the SSD. OTOH, those who were using a Velociraptor (or RAID array) for boot and another drive for storage will see their power consumption decrease.
sawyeriii - Wednesday, March 18, 2009 - link
Have you used a SSD? (If so which)I would state that it is not a luxary product, it is a premium product. The price difference you pay WILL translate to faster performance (if you choose correctly). More RAM only helps upto a point.
Remember performance is based on a system of parts...
CPU
RAM
NORTHBRIDGE
GPU
SOUTHBRIDGE
I/O INTERFACE
HDD/SDD
Microsoft's Windows Experience Index has specific flaws, but the concept is sound... The system can only go a fast as the slowest component in the system (relative to the amount of time used by that component).
Testtest - Wednesday, March 18, 2009 - link
... there's also Supertalent's Ultradrive ME (MLC) and LE (SLC) and Photofast's G-Monster v3At least the Supertalent drives are quite a bit cheaper with the same drive layout/controller than the Vertex drives and only differ in the firmware (which isn't bad either).
It's however possible at least with the Ultradrive ME currently to provoke a kinda timeout error after they've been fully filled once and then still beeing written on. I don't own a Vertex so I can't test that there but if it was a controller issue, it should pop up there sooner or later as well (if you take a look in their suppport forum some error reports seem very similar).
Intels have their 80% bug, Indilinx drives have their issues too it seems - let's hope that firmware can cure it!
Great article btw!
iwod - Thursday, March 19, 2009 - link
Both SuperTalent and OCZ 30 / 32 GB drive cost exactly the same on NewEgg$129