Re: 3 x PostgreSQL in cluster/redunant

On Tuesday 2005-11-15 13:06, Joshua D. Drake wrote:
> Michelle Konzack wrote:
> > Am 2005-11-14 16:54:41, schrieb Jim C. Nasby:
> >> On Mon, Nov 14, 2005 at 07:36:44PM +0100, Michelle Konzack wrote:
> >>> Hello *,
> >>>
> >>> I have three Sun Server where I have reserved on each Server a Raid-5
> >>> of 1 TByte for my PostgreSQL.  The first PostgreSQL is up and running
> >>> with a database of 150 GByte.
> >>
> >> Keep in mind that databases and RAID5 generally don't mix very well.
> >
> > Can you explain me why?
>
> RAID 5 is very expensive for writes.
>
> > Unfortunatly the Controllers in the three SUN-Servers do not support
> > 300 GByte SCSI-Drives, so I have to continue with the Raid-5 of 16x
> > 76 GByte.
>
> Could you do RAID 10?
>
> Sincerely,
>
> Joshua D. Drake

I've seen books on tuning recommend RAID-5 into the low terrabyte range for
read-dominated databases (notably small data warehouse applications).

For very large multi-terrabye applications the suggestion is that RAID-50
along with streaming to and from stochastically accessed distributed storage
can partially hide the expense of writing to storage while bringing the money
cost of storage down considerably.