Re: Can anyone explain this pgbench results?

On Tue, Mar 07, 2006 at 08:49:30PM +0100, Joost Kraaijeveld wrote:
>
> Jim C. Nasby wrote:
>
> > Speaking of 'disks', what's your exact layout? Do you have a 5 drive
> > raid5 for the OS and the database, 1 drive for swap and 1 drive for
> > pg_xlog?
>
> On a Sil SATA 3114 controller:
> /dev/sda OS + Swap
> /dev/sdb /var with pg_xlog
>
> On the 3Ware 9500S-8, 5 disk array:
> /dev/sdc with the database (and very safe, my MP3 collection ;-))
>
> As I wrote in one of my posts to Michael, I suspect that the card is not handling the amount of write operations as well as I expected. I wonder if anyone else sees the same characteristics with this kind of card.

Well, the problem is that you're using RAID5, which has a huge write
overhead. You're unlikely to get good performance with it.

Also, it sounds like sda and sdb are not mirrored. If that's the case,
you have no protection from a drive failure taking out your entire
database, because you'd lose pg_xlog.

If you want better performance your best bets are to either setup RAID10
or if you don't care about the data, just go to RAID0.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461