Re: Weird XFS WAL problem

Craig James wrote:
> I'm testing/tuning a new midsize server and ran into an inexplicable
> problem. With an RAID10 drive, when I move the WAL to a separate
> RAID1 drive, TPS drops from over 1200 to less than 90!

Normally <100 TPS means that the write cache on the WAL drive volume is
disabled (or set to write-through instead of write-back). When things
in this area get fishy, I will usually download sysbench and have it
specifically test how many fsync calls can happen per second.
http://projects.2ndquadrant.com/talks , "Database Hardware
Benchmarking", page 28 has an example of the right incantation for that.

Also, make sure you run 3ware's utilities and confirm all the disks have
finished their initialization and verification stages. If you just
adjusted disk layout that and immediate launched into benchmarks, those
are useless until the background cleanup is done.

--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.us