On 06/16/2011 03:04 PM, Merlin Moncure wrote:
I don't necessarily agree. the drives are SLC and have the potential to have a much longer lifespan than any MLC drive, although this is going to depend a lot on the raid controller if write caching is disabled. Also, reading the post that got all this started (http://www.mysqlperformanceblog.com/2009/03/02/ssd-xfs-lvm-fsync-write-cache-barrier-and-lost-transactions/), the OP was able to configure them to run durably with 1200 write iops.
We've also seen http://petereisentraut.blogspot.com/2009/07/solid-state-drive-benchmarks-and-write.html where Peter was only able to get 441 seeks/second on the bonnie++ mixed read/write test that way. And no one has measured the longevity of the drive when it's running in this mode. A large portion of the lifespan advantage MLC would normally have over SLC goes away if it can't cache writes anymore. Worst-case, if the drive is always hit with 8K writes and the erase size is 128KB, you might get only 1/16 of the specified lifetime running it cacheless.
I just can't recommend that people consider running one of these in a mode it was never intended to. The fact that the consumer drives from this generation still lose data even with the write cache turned off should make you ask what other, more difficult to trigger failure modes are still hanging around the enterprise drives, too. Everyone I've seen suffer through problems with these gave up on them before even trying really in-depth reliability tests, so I don't consider that territory even very well explored.
-- Greg Smith 2ndQuadrant US greg@xxxxxxxxxxxxxxx Baltimore, MD PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us "PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
