On Tue, 6 Nov 2007, Dimitri Fontaine wrote:
> Some knowing-better-than-me people on #postgresql had the remark that
> depending on the write transaction volumes (40 to 60 percent of my tps, but
> no so much for this hardware), I could somewhat benefit in setting the WAL on
> the OS raid1, and having 8 raid10 disks for data
That really depends on the write volume to the OS drive. If there's lots
of writes there for things like logs and temporary files, the disruption
to the WAL writes could be a problem. Part of the benefit of having a
separate WAL disk is that the drive never has to seek somewhere to write
anything else.
Now, if instead you considered putting the WAL onto the database disks and
adding more disks to the array, that might work well. You'd also be
losing something because the WAL writes may have to wait behind seeks
elsewhere. But once you have enough disks in an array to spread all the
load over that itself may improve write throughput enough to still be a
net improvement.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD