On Sat, 24 Dec 2005, Ron wrote:
At 02:50 PM 12/24/2005, Frank Wiles wrote:
Juan Casero <caseroj@xxxxxxxxxxx> wrote:
> Sorry folks. I had a couple of glasses of wine as I wrote this.
> Anyway I originally wanted the box to have more than two drives so I
> could do RAID 5 but that is going to cost too much. Also, contrary
> to my statement below it seems to me I should run the 32 bit
> postgresql server on the 64 bit kernel. Would you agree this will
> probably yield the best performance? I know it depends alot on the
> system but for now this database is about 20 gigabytes. Not too large
> right now but it may grow 5x in the next year.
You definitely DO NOT want to do RAID 5 on a database server. That
is probably the worst setup you could have, I've seen it have lower
performance than just a single hard disk.
RAID 1 and RAID 1+0 are optimal, but you want to stay far away from
RAID 5. IMHO RAID 5 is only useful on near line backup servers or
Samba file servers where space is more important than speed.
That's a bit misleading. RAID 5 excels when you want read speed but don't
care as much about write speed. Writes are typical ~2/3 the speed of reads
on a typical decent RAID 5 set up.
So if you have tables that are read often and written to rarely or not at
all, putting them on RAID 5 is optimal. In both data mining like and OLTP
like apps there are usually at least some such tables.
raid 5 is bad for random writes as you state, but how does it do for
sequential writes (for example data mining where you do a large import at
one time, but seldom do other updates). I'm assuming a controller with a
reasonable amount of battery-backed cache.
David Lang
