Henry C. wrote:
> I believe this perception that SSDs are less "safe" than failure-prone
> mechanical hard drives will eventually change.
>
Only because the manufacturers are starting to care about write
durability enough to include the right hardware for it. Many of them
are less safe right now on some common database tasks. Intel's gen 1
and gen 2 drives are garbage for database use. I've had customers lose
terabytes of data due to them. Yes, every system can fail, but these
*will* fail and corrupt your database the first time there's a serious
power problem of some sort. And the idea that a UPS is sufficient to
protect against that even happening in wildly optimistic.
See http://wiki.postgresql.org/wiki/Reliable_Writes for more background
here, and links to reading on the older Intel drives. I summarized the
situation with their newer 320 series drives at
http://blog.2ndquadrant.com/en/2011/04/intel-ssd-now-off-the-sherr-sh.html
Those finally get the write flushing right. But the random seeks IOPS
is wildly lower than you might expect on read/write workloads. My own
tests and other sources have all come up with around 3500 IOPS as being
a real-world expectation for the larger sizes of these drives. Also, it
is cheap flash, so durability in a server environment won't be great.
Don't put your WAL on them if you have a high transaction rate. Put
some indexes there instead.
--
Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books