Re: improving write performance for logging

On Fri, Jan 06, 2006 at 09:00:06AM -0500, Ian Westmacott wrote:
> On Thu, 2006-01-05 at 19:08 -0600, Jim C. Nasby wrote:
> > On Wed, Jan 04, 2006 at 11:00:38AM -0500, Ian Westmacott wrote:
> > > The WAL is a 2-spindle (SATA) RAID0 with its own controller (ext3).
> > > The tables are on a 10-spindle (SCSI) RAID50 with dual U320
> > > controllers (XFS). This is overkill for writing and querying the data,
> > > but we need to constantly ANALYZE and VACUUM in the
> > > background without interrupting the inserts (the app is 24x7). The
> > > databases are 4TB, so these operations can be lengthy.
> >
> > How come you're using RAID50 instead of just RAID0? Or was WAL being on
> > RAID0 a typo?
>
> We use RAID50 instead of RAID0 for the tables for some fault-tolerance.
> We use RAID0 for the WAL for performance.
>
> I'm missing the implication of the question...

The problem is that if you lose WAL or the data, you've lost everything.
So you might as well use raid0 for the data if you're using it for WAL.
Or switch WAL to raid1. Actually, a really good controller *might* be
able to do a good job of raid5 for WAL. Or just use raid10.
--
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