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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zdzichu - Sunday, March 22, 2009 - link
Very nice and thorough article. I only lack more current status of TRIM command support in current operating systems. For example, Linux supports it since last year:http://kernelnewbies.org/Linux_2_6_28#head-a1a9591...">http://kernelnewbies.org/Linux_2_6_28#h...a9591f48...
Sinned - Sunday, March 22, 2009 - link
Outstanding article that really helped me understand SSD drives. I wonder how much of an impact the new SATA III standard will have on SSD drives? I believe we are still at the beginning stage for SSD drives and your article shows that much more work needs to be done. My respect for OCZ and how they responded in a positive and productive way should be a model for the rest of the SSD makers. Thank you again for such a concise article.Respectfully,
Sinned
529th - Sunday, March 22, 2009 - link
The first thing I thought of was Democracy. Don't know why. Maybe it was because a company listened to our common goal of performance. Thank you OCZ for listening, I'm sure it will pay off!!!araczynski - Saturday, March 21, 2009 - link
very nice read. the 4/512 issue seems a rather stupid design decision, or perhaps more likely a stupid problem to find this 4/512 solution as 'acceptable'.although a great marketing choice, built in automatic life expectancy reduction.
sounds like the manufacturers want the hard drives to become a disposable medium like styrofoam cups.
perhaps when they narrow the disparity down to 4/16, i might consider buying an ssd. that, or when they beat the 'old school' physical platters in price.
until then, get back to the drawing board and stop crapping out these half arsed 'should be good enough' solutions.
IntelUser2000 - Sunday, March 22, 2009 - link
araczynski: The 4/512 isn't done by accident. It's done to lower prices. The flash technology used in SSDs are meant to replace platter HDDs in the future. There's no way of doing that without cost reductions like these. Even with that the SSDs still cost several times more per storage space.araczynski - Tuesday, March 24, 2009 - link
i understand that, but i don't remember original hard drives being released and being slower than the floppy drives they were replacing.this is part of the 'release beta' products mentality and make the consumer pay for further development.
the 5.25" floppy was better than the huge floppy in all respects when it was released. the 3.5" floppy was better than the 5.25" floppy when it was released. the usb flash drives were better than the 3.5" floppies when they were released.
i just hate the way this is being played out at the consumer's expense.
hellcats - Saturday, March 21, 2009 - link
Anand,What a great article. I usually have to skip forwards when things bog down, but they never did with this long, but very informative article. Your focus on what matters to users is why I always check anandtech first thing every morning.
juraj - Saturday, March 21, 2009 - link
I'm curious what capacity is the OCZ Vertex drive reviewed. Is it an 120 / 250g drive or supposedly slower 30 / 60g one?Symbolics - Friday, March 20, 2009 - link
The method for generating "used" drives is flawed. For creating a true used drive, the spare blocks must be filled as well. Since this was not done, the results are biased towards the Intel drives with their generous amount of spare blocks that were *not* exhausted when producing the used state. An additional bias is introduced by the reduction of the IOmeter write test to 8 GB only. Perhaps there are enough spare blocks on the Intel drives so that these 8 GB can be written to "fresh" blocks without the need for (time-consuming) erase operations.Apart from these concerns, I enjoyed reading the article.
unknownError - Saturday, March 21, 2009 - link
I also just created an account to post, very nice article!Lots of good well thought out information, I'm so tired of synthetic benchmarks glad someone goes through the trouble to bench these things right (and appears to have the education to really understand them). Whats with the grammar police though? geez...