On Sat, Aug 29, 2009 at 2:46 AM, Greg Stark<gsst...@mit.edu> wrote: > On Sat, Aug 29, 2009 at 5:20 AM, Luke Koops<luke.ko...@entrust.com> wrote: >> Joseph S Wrote >>> If I have 14 drives in a RAID 10 to split between data tables >>> and indexes what would be the best way to allocate the drives >>> for performance? >> >> RAID-5 can be much faster than RAID-10 for random reads and writes. It is >> much slower than RAID-10 for sequential writes, but about the same for >> sequential reads. For typical access patterns, I would put the data and >> indexes on RAID-5 unless you expect there to be lots of sequential scans. > > That's pretty much exactly backwards. RAID-5 will at best slightly > slower than RAID-0 or RAID-10 for sequential reads or random reads. > For sequential writes it performs *terribly*, especially for random > writes. The only write pattern where it performs ok sometimes is > sequential writes of large chunks.
Note that while RAID-10 is theoretically always better than RAID-5, I've run into quite a few cheapie controllers that were heavily optimised for RAID-5 and de-optimised for RAID-10. However, if it's got battery backed cache and can run in JBOD mode, linux software RAID-10 or hybrid RAID-1 in hardware RAID-0 in software will almost always beat hardware RAID-5 on the same controller. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
