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
New vs Used SSD Performance
We begin our look at how the overhead of managing pages impacts SSD performance with iometer. The table below shows iometer random write performance; there are two rows for each drive, one for “new” performance after a secure erase and one for “used” performance after the drive has been well used.
| 4KB Random Write Speed | New | "Used" |
| Intel X25-E | 31.7 MB/s | |
| Intel X25-M | 39.3 MB/s | 23.1 MB/s |
| JMicron JMF602B MLC | 0.02 MB/s | 0.02 MB/s |
| JMicron JMF602Bx2 MLC | 0.03 MB/s | 0.03 MB/s |
| OCZ Summit | 12.8 MB/s | 0.77 MB/s |
| OCZ Vertex | 8.2 MB/s | 2.41 MB/s |
| Samsung SLC | 2.61 MB/s | 0.53 MB/s |
| Seagate Momentus 5400.6 | 0.81 MB/s | - |
| Western Digital Caviar SE16 | 1.26 MB/s | - |
| Western Digital VelociRaptor | 1.63 MB/s | - |
Note that the “used” performance should be the slowest you’ll ever see the drive get. In theory, all of the pages are filled with some sort of data at this point.
All of the drives, with the exception of the JMicron based SSDs went down in performance in the “used” state. And the only reason the JMicron drive didn’t get any slower was because it is already bottlenecked elsewhere; you can’t get much slower than 0.03MB/s in this test.
These are pretty serious performance drops; the OCZ Vertex runs at nearly 1/4 the speed after it’s been used and Intel’s X25-M can only crunch through about 60% the IOs per second that it did when brand new.
So are SSDs doomed? Is performance going to tank over time and make these things worthless?
"Used" SSD performance vs. conventional hard drives.
Pay close attention to the average write latency in the graph above. While Intel’s X25-M pulls an extremely fast sub-0.3ms write latency normally, it levels off at 0.51ms in its used mode. The OCZ Vertex manages a 1.43ms new and 4.86ms used. There’s additional overhead for every write but a well designed SSD will still manage extremely low write latencies. To put things in perspective, look at these drives at their worst compared to Western Digital’s VelociRaptor.The degraded performance X25-M still completes write requests in around 1/8 the time of the VelociRaptor. Transfer speeds are still 8x higher as well.
Note that not all SSDs see their performance drop gracefully. The two Samsung based drives perform more like hard drives here, but I'll explain that tradeoff much later in this article.
How does this all translate into real world performance? I ran PCMark Vantage on the new and used Intel drive to see how performance changed.
| PCMark Overall Score | New | "Used" | % Drop |
| Intel X25-M | 11902 | 11536 | 3% |
| OCZ Summit | 10972 | 9916 | 9.6% |
| OCZ Vertex | 11253 | 9836 | 14.4% |
| Samsung SLC | 10143 | 9118 | 10.1% |
| Seagate Momentus 5400.6 | 6817 | - | - |
| Western Digital VelociRaptor | 7500 | - | - |
The real world performance hit varies from 0 - 14% depending on the drive. While the drives are still faster than a regular hard drive, performance does drop in the real world by a noticeable amount. The trim command would keep the drive’s performance closer to its peak for longer, but it would not have prevented this from happening.
| PCMark Vantage HDD Test | New | "Used" | % Drop |
| Intel X25-M | 29879 | 23252 | 22% |
| JMicron JMF602Bx2 MLC | 11613 | 11283 | 3% |
| OCZ Summit | 25754 | 16624 | 36% |
| OCZ Vertex | 20753 | 17854 | 14% |
| Samsung SLC | 17406 | 12392 | 29% |
| Seagate Momentus 5400.6 | 3525 | - | |
| Western Digital VelociRaptor | 6313 | - |
HDD specific tests show much more severe drops, ranging from 20 - 40% depending on the drive. Despite the performance drop, these drives are still much faster than even the fastest hard drives.
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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 :)