Re: Postgres on RAID5

Alex Turner wrote:
> I would recommend running a bonnie++ benchmark on your array to see if
> it's the array/controller/raid being crap, or wether it's postgres.  I
> have had some very surprising results from arrays that theoretically
> should be fast, but turned out to be very slow.
>
> I would also seriously have to recommend against a 14 drive RAID 5!
> This is statisticaly as likely to fail as a 7 drive RAID 0 (not
> counting the spare, but rebuiling a spare is very hard on existing
> drives).

Thanks for the reply.

Here are the results of the bonnie test on my array:

./bonnie -s 10000 -d . > oo 2>&1
File './Bonnie.23736', size: 10485760000
Writing with putc()...done
Rewriting...done
Writing intelligently...done
Reading with getc()...done
Reading intelligently...done
Seeker 1...Seeker 2...Seeker 3...start 'em...done...done...done...
        -------Sequential Output-------- ---Sequential Input-- --Random--
        -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
     MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
  10000 4762  96.0 46140 78.8 31180 61.0 3810  99.9 71586 67.7 411.8 13.1

On a different note, I am not sure how the probability of RAID5 over 15
disks failing is the same as that of a RAID0 array over 7 disks. RAID5
can operate in a degraded mode (14 disks - 1 bad), RAID0 on the other
hand cannot operate on 6 disks (6 disks - 1 bad). Am I missing something?

Are you saying running RAID0 on a set of 2 RAID1  arrays of 7 each? That
would work fine, except I cannot afford to "loose" that much space.

Care to comment on these numbers? Thanks.



Arshavir