Re: Disk configurations....

On Thursday 24 January 2008, Nathan Wilhelmi <wilhelmi(at)ucar(dot)edu> wrote:
> Hello - Typically case of a software guy needing to spec hardware for a
> new DB server. Further typified case of not knowing exact amount of data
> and I/O patterns. So if you were to spec a disk system for a new general
> purpose PostgreSQL server any suggestions of what to start with?
>
> Details I have:
>
> 1) We think 500GB is enough storage for the DB.
> 2) I would guess 66% read 33% write patterns, maybe closer to 50/50.
>
> I would assume that we would want to go SCSI raid. Would you do the
> whole disk array as Raid 5 or whole you partition it up differently?
> Would you go with 3x300gb disks or would you use more smaller disks to
> get there?

RAID-5 is probably about the worst choice for a high-write activity
database. Certainly pg_log should not be on a RAID-5 array. Also, RAID-5 is
worse on smaller arrays than larger arrays.

SCSI (or SAS) is probably only worthwhile if you need 15K RPM drives.

More disks are usually better than fewer expensive disks.

Personally, I would get 8 new SATA-II drives, put them on a good SAS
controller with a battery-protected write-back cache, and set them up in
RAID-10. If you later find out you need more IOPs you can replace them with
15K RPM SAS drives without throwing out the rest of the server.

Without any idea as to your transaction volume, though, this is a very
general recommendation.

--
Alan