Re: Query plan looks OK, but slow I/O - settings advice?

On Tue, 2005-08-16 at 10:46 -0700, Roger Hand wrote:
> The disks are ext3 with journalling type of ordered, but this was later changed to writeback with no apparent change in speed.
>
> They're on a Dell poweredge 6650 with LSI raid card, setup as follows:
> 4 disks raid 10 for indexes (145GB) - sdc1
> 6 disks raid 10 for data (220GB) - sdd1
> 2 mirrored disks for logs - sdb1
>
> stripe size is 32k
> cache policy: cached io (am told the controller has bbu)
> write policy: write-back
> read policy: readahead

I assume you are using Linux 2.6. Have you considered booting your
machine with elevator=deadline? You can also change this at runtime
using sysfs.

These read speeds are not too impressive. Perhaps this is a slow
controller. Alternately you might need bigger CPUs.

There's a lot of possibilities, obviously :) I'd start with the
elevator, since that's easily tested.

-jwb