On 2013-11-06 20:25, Mike Dawson wrote:
We just fixed a performance issue on our cluster related to spikes
of high latency on some of our SSDs used for osd journals. In our case,
the slow SSDs showed spikes of 100x higher latency than expected.
Many SSDs show this behaviour when 100% provisioned and/or never
TRIM'd, since the pool of ready erased cells is quickly depleted under
steady write workload, so it has to wait for cells to charge to
accommodate the write.
The Intel 3700 SSDs look to have some of the best consistency ratings
of any of the more reasonably priced drives at the moment, and good IOPS
too:
http://www.intel.com/content/www/us/en/solid-state-drives/solid-state-drives-dc-s3700-series.html
Obviously the quoted IOPS numbers are dependent on quite a deep queue
mind.
There is a big range of performance in the market currently; some
Enterprise SSDs are quoted at just 4,000 IOPS yet cost as many pounds!
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