On 11/06/2013 03:35 PM, james@xxxxxxxxxxxx wrote:
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!
Most vendors won't give you DC S3700s by default, but if you put your
foot down most of them seem to have SKUs for them lurking around
somewhere. Right now they are the first drive I recommend for journals,
though I believe some of the other vendors may have some interesting
options in the future too.
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