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
Simulating a Used Drive
Since SSD performance degrades over time, it’s important to not only look at how well these drives perform new - but also the worst they’d perform over their lifetime. In order to do so we’d need a repeatable way of “seasoning” a drive to reduce its performance to the worst it could possibly get. The most realistic worst-case scenario is one where every single block on the drive is full of data. If a secure erase wipes all LBAs, that’s the best place to start. To simulate a well seasoned drive I first secure erased the drive.
After the secure erase, I used iometer to write one contiguous file across the disk - filling up the entire drive with 128KB blocks. In the case of the 80GB Intel X25-M, that’s 74.5GB of data on the drive before I run a single benchmark. The spare area is left untouched.
Next, I take my test image and I restore it onto the partition with a sector by sector copy. The sequential file write made sure that data is stored in every page of the SSD, the test image restore adds a twist of randomness (and realism) to the data.
There are other ways to produce a drive in its well-used state, but this ends up being the most consistent and repeatable. To confirm that my little simulation does indeed produce a realistically worn drive I ran PCMark on three different drives: 1) a freshly secure-erased Intel X25-M, 2) an Intel X25-M setup using the method I just described and 3) the Intel X25-M used in my CPU testbed that has been through hundreds of SYSMark runs.
The benchmark of choice is PCMark Vantage; it simulates the real world better than most drive benchmarks. The results are below:
| Intel X25-M State | PCMark Vantage Overall Test | PCMark Vantage HDD Test |
| Fresh Secure Erase | 11902 | 29879 |
| Simulated Used Drive | 11536 | 23252 |
| Actual Testbed Used Drive | 11140 | 23438 |
The secure erased system loses about 3% of its overall performance and 22% of its hard drive specific performance compared to my testbed drive. The seasoning method I described above produces a drive with nearly identical drops in performance.
The method appears to be sound.
Now that we have a way of simulating a used drive, let’s see how the contestants fared.
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Luddite - Friday, March 20, 2009 - link
So even with the TRIM command, when working with large files, say, in photoshop and saving multiple layers, the performance will stil drop off?proviewIT - Thursday, March 19, 2009 - link
I bought a Vertex 120GB and it is NOT working on my Nvidia chipsets motherboard. Anyone met the same problem? I tried intel chipsets motherboard and seems ok.I used HDtach to test the read/write performance 4 days ago, wow, it was amazing. 160MB/s in write. But today I felt it slower and used HDtach to test again, it downs to single digit MB per second. Can I recover it or I need to return it?
kmmatney - Thursday, March 19, 2009 - link
Based on the results and price, I would say that the OCZ Vertex deserves a Editor's choice of some sort (Gold, Silver)...Tattered87 - Thursday, March 19, 2009 - link
While I must admit I skipped over some of the more technical bits where SSD was explained in detail, I read the summaries and I've gotta admit this article was extremely helpful. I've been wanting to get one of these for a long time now but they've seemed too infantile in technological terms to put such a hefty investment in, until now.After reading about OCZ's response to you and how they've stepped it up and are willing to cut unimportant statistics in favor of lower latencies, I actually decided to purchase one myself. Figured I might as well show my appreciation to OCZ by grabbing up a 60GB SSD, not to mention it looks like it's by far the best purchase I can make SSD-wise for $200.
Thanks for the awesome article, was a fun read, that's for sure.
bsoft16384 - Thursday, March 19, 2009 - link
Anand, I don't want to sound too negative in my comments. While I wouldn't call them unusable, there's no doubt that the random write performance of the JMicron SSDs sucks. I'm glad that you're actually running random I/O tests when so many other websites just run HDTune and call it a day.That X25-M for $340 is looking mighty tempting, though.
MrSpadge - Thursday, March 19, 2009 - link
Hi,first: great article, thanks to Anand and OCZ!
Something crossed my mind when I saw the firmware-based trade-off between random writes and sequential transfer rates: couldn't that be adjusted dynamically to get the best of both worlds? Default to the current behaviour but switch into something resembling te old one when extensive sequential transfers are detected?
Of course this neccesiates that the processor would be able to handle additional load and that the firmware changes don't involve permanent changes in the organization of the data.
Maybe the OCZ-Team already thought about this and maybe nobody's going to read this post, buried deep within the comments..
MrS
Per Hansson - Thursday, March 19, 2009 - link
Great work on the review AnandI really enjoyed reading it and learning from it
Will there be any tests of the old timers like Mtron etc?
tomoyo - Thursday, March 19, 2009 - link
That was kind of strange to me too. But I assume Anand really means the desktop market, not the server storage/business market. Since it's highly doubtful that the general consumer will spend many times as much money for 15k SAS drives.Gary Key - Thursday, March 19, 2009 - link
The intent was based it being the fastest for a consumer based desktop drive, the text has been updated to reflect that fact.tomoyo - Thursday, March 19, 2009 - link
I've always been someone who wants real clarify and truth to the information on the internet. That's a problem because probably 90% of things are not. But Anand is one man I feel a lot of trust for because of great and complete articles such as this. This is truly the first time that I feel like I really understand what goes into ssd performance and why it can be good or bad. Thank you so much for being the most inciteful voice in the hardware community. And keep fighting those damn manufacturers who are scared of the facts getting in the way of their 200MB/s marketing bs.