Re: [PERFORM] best arrangement of 3 disks for (insert) performance

On Sat, 2003-09-13 at 23:44, Cott Lang wrote:
> > Having WAL on a separate drive from the database would be something of
> > a win. I'd buy that 1 disk for OS+WAL and then RAID [something]
> > across the other two drives for the database would be pretty helpful.
>
> Just my .02,
>
> I did a lot of testing before I deployed our ~50GB postgresql databases
> with various combinations of 6 15k SCSI drives. I did custom benchmarks
> to simulate our applications, I downloaded several benchmarks, etc.
>
> It might be a fluke, but I never got better performance with WALs on a
> different disk than I did with all 6 disks in a 0+1 configuration.
> Obviously that's not an option with 3 disks. =)

Interesting. Where did you put the OS, and what kind of, and how
many, SCSI controllers did you have?

PCI 32bit/33MHz or 64bit/66MHz PCI? 32bit/33MHz PCI has a max
throughput of 132MB/s, which is 60% smaller than the theoretical
bandwidth of U320 SCSI, so maybe you were saturating the PCI bus,
and that's why a separate WAL didn't show any improvement?

(If the WAL ever becomes the vehicle for PITR, then it will have
to be on a separate disk [and preferably a separate controller],
even if it slows performance.)

--
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