Hi!
> -----Ursprüngliche Nachricht-----
> Von: Shridhar Daithankar [mailto:shridhar_daithankar@persistent.co.in]
> Gesendet: Dienstag, 21. Oktober 2003 08:08
> An: pgsql-general@postgresql.org
> Betreff: Re: [GENERAL] Recomended FS
> Can you compare ogbench results for the RAID and single IDE
> disks? It would be
> great if you could turn off write caching of individual
> drives in RAID and
> test it as well.
One thing I can say from previous experiences is that the type of RAID
does matter quite a lot. RAID5, even with a quite expensive Adaptec
SCSI-hardware-controller, is not always the best solution for a
database, particularly if there's a lot of INSERTs and UPDATEs going on.
If you're not too dependant on raw storage size, your best bet is to use
the space-consuming RAID0+1 instead; the reasoning behind this is
probably that on RAID5 the controller has to calculate the parity-data
for every write-access, on RAID0+1 it just mirrors and distributes the
data, reducing overall load on the controller and making use of more
spindles and two-channel-SCSI.
We're hosting some DB-intensive websites (>12M impressions/month) on two
PostgreSQL-servers (one DELL Poweredge 6400, 4xPentium III Xeon@550MHz,
2GB RAM, 4x18GB SCSI in RAID0+1, 1 hot-spare and one Dell Poweredge
6650, 4x Intel XEON@1.40GHz, 4GB RAM, 4x36 GB SCSI in RAID0+1, 1
hot-spare) and when I switched the 5-disc-RAID5-config over to a
4-disc-RAID0+1 plus one hotspare, I noticed system-load dropping by a
very considerable amount. I haven't got any benchmark-figures to show
off though, it's just experiences from a realworld application.
Regards
Markus