Re: Considering Solid State Drives

Allan Kamau wrote:
> I am now thinking of investing in a SSD (Solid State Drive), and maybe
> choosing between "Crucial Technology 256GB Crucial M225 Series
> 2.5-Inch Solid State Drive (CT256M225)" and "Intel X25-M G2 (160GB) -
> Intel MLC".

Both of these are worthless for database applications if you care about
your data. In order to perform well, SSDs need to have a write cache to
buffer small writes. For PostgreSQL to work as intended, that write
cache needs to be non-volatile. It is not in either of those drives. I
hear tales of lost PostgreSQL data on Intel SSDs every month, the
database is lucky to survive a single power outage.

The only relatively inexpensive SSD we've heard about on the Performance
list that's survived all of the durability on crash tests thrown at it
is the OCZ Vertex 2 Pro; see
http://archives.postgresql.org/pgsql-performance/2010-07/msg00449.php
for a summary. That avoids this problem by having an Ultracapacitor
integrated with the drive, to allow orderly processing of the write
cache if power is lost. There are other SSD devices that are similarly
reliable, but the costs are quite a bit higher.

More background about this topic at
http://wiki.postgresql.org/wiki/Reliable_Writes

--
Greg Smith 2ndQuadrant US greg(at)2ndQuadrant(dot)com Baltimore, MD
PostgreSQL Training, Services and Support www.2ndQuadrant.us
"PostgreSQL 9.0 High Performance": http://www.2ndQuadrant.com/books