I've already learned my lesson and will never use raid 5 again. The
question is what I do with my 14 drives. Should I use only 1 pair for
indexes or should I use 4 drives? The wal logs are already slated for
an SSD.
Scott Marlowe wrote:
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
