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
SSD Aging: Read Speed is Largely Unaffected
Given the nature of the SSD performance-over-time “problem” you’d expect to only pay the performance penalty when writing files, not reading. And for once, I don’t have any weird exceptions to talk about - this is generally the case.
The table below shows sequential read performance for 2MB blocks on new vs. “used” SSDs. I even included data for a couple of the hard drives in the "Used" column; for those numbers I'm simply measuring transfer rates from the slowest parts of the platter:
| 2MB Sequential Read Speed | New | "Used" |
| Intel X25-E | 240.1 MB/s | |
| Intel X25-M | 264.1 MB/s | 230.2 MB/s |
| JMicron JMF602B MLC | 134.7 MB/s | 134.7 MB/s |
| JMicron JMF602Bx2 MLC | 164.1 MB/s | 164.1 MB/s |
| OCZ Summit | 248.6 MB/s | 208.6 MB/s |
| OCZ Vertex | 257.8 MB/s | 250.1 MB/s |
| Samsung SLC | 101.4 MB/s | |
| Seagate Momentus 5400.6 | 77.9 MB/s | - |
| Western Digital Caviar SE16 | 104.6 MB/s | 54.3 MB/s |
| Western Digital VelociRaptor | 118.0 MB/s | 79.2 MB/s |
The best SSDs still transfer data at over 2x the rate of the VelociRaptor.
Read latency is also extremely good on these worn SSDs:
I left the conventional hard drives out of the chart simply because they completely screw up the scale. The VelociRaptor has a latency of 7.2ms in this iometer test with a queue depth of 3 IOs; that's an order of magnitude slower than the slowest SSD here.
Since you only pay the overhead penalty when you go to write to a previously-written block, the performance degradation only really occurs when you’re writing - not when you’re reading.
Now your OS is always writing to your drive, and that’s why we see a performance impact even if you’re just launching applications and opening files and such, but the penalty is much less tangible when it comes to read performance.
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Jamor - Wednesday, March 18, 2009 - link
The best tech article I've ever read, and I've read a few.haze4peace - Wednesday, March 18, 2009 - link
Wow, excellent article and so much useful information in an easy to understand way. I have just recently been paying attention to SSDs and thanks to this article I am armed with the information to make the correct choice for my needs. Thanks AnandTech, its the deep and honest articles like these that keep me coming back for more.Alseki - Wednesday, March 18, 2009 - link
I just registered then simply to say, great article. Really informative and enjoyable to read.alexsch8 - Wednesday, March 18, 2009 - link
Anand,Thank you for this article, very informative.
Looking at the example you are giving with your self-manufactured SSD drive: If I save the DOC I use up a page. Based on what you are saying, if I make a change to that DOC, it would then be saved in the next page instead of overwriting the existing page? If that is true, then the File Allocation system (FAT or MFT) itself would contribute quite a bit to the 'filling up of pages' phenomena. Could you elaborate if the proposed file system for SSD addresses this?
Ytterbium - Wednesday, March 18, 2009 - link
Fantastic article, shame that the vendors blacklisted you for telling the truth and OCZ rock for working so hard to address issues.I'll be ordering my Intel SSD soon, I'll defintly consider the Summit when it comes out for my encoding rig as there sequental writes matter to me.
mindless1 - Wednesday, March 18, 2009 - link
Great even, but I've have to disagree with the significance of the passage that suggested the Indilinx controller makes data loss as bad on those SSD as on a conventional hard drive.The primary cause of data loss is mechanical or component failure, not power loss. If we want to consider power loss, it's not just the drive which is prone to lose data, the entire system memory suffers far more data loss than that.
Further, a sufficiently sized supercapacitor should keep the drive operating for a period of time beyond when the rest of the system would be operational, it could be sufficient for the controller to finish writing to flash all received data (or just use an UPS, that's what they're for?).
Second, I can't believe that OCZ only tests designs with HDTach and Atto, I think it more likely they knew of the problem but didn't expect anyone to find it so quickly, and felt the higher sequential speeds made it more marketable. This makes me feel that manufacturers, then online sellers should differentiate their drives with a standardized random read/write score.
What would be really nice is if the Indilinx based SSDs had an application available, similar to a HDD acoustic management bit changing app, that lets the owner set their own preference for IO versus sequential read performance.
gomakeit - Wednesday, March 18, 2009 - link
This is by far the BEST article on SSD I've ever read! Great job anand and yes I read every single word of it!MagicPants - Wednesday, March 18, 2009 - link
Don't they ever try using their own devices? One second of latency should slap any user in the face. It should be very easy for a manufacturer to build a system with their new technology put it in front of people and see what happens, but apparently they're not doing this.They wait for reviewers to do the work for them and then get upset when they find a problem.
What the manufacturers should be taking away from this article is:
1) Try your competitor's products
2) Try your own products
3) Try them in real life as opposed to synthetic tests
4) Compare everything you've tried and market the performance that matters
7Enigma - Thursday, March 19, 2009 - link
But that would make sense....and we know marketing rarely does.paulinus - Wednesday, March 18, 2009 - link
That art is great. Finally someone done ssd test's right, and said loud what we, customers, can get for that hefty pricetags.I've supposed that only choices are intel and new ocz's. Now I know, and big kudos for that.
Just need a bit more $$ for x25-m, it'll be ideal for heavy workstation use, and biggest vertex'll replace wd black in my aging 6910p :)