The SSD Anthology: Understanding SSDs and New Drives from OCZby Anand Lal Shimpi on March 18, 2009 12:00 AM EST
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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.