Disk IO issues

[FD Cami]

On Sun, 4 Jan 2009 11:59:38 -0600 (CST)
Mike McGrath <mmcgrath at redhat.com> wrote:

> On Sat, 3 Jan 2009, Matt Domsch wrote:
> 
> > On Sun, Jan 04, 2009 at 03:02:55AM +0000, Kostas Georgiou wrote:
> > 
> > Mike, your tests were all on the local file system, not across an NFS
> > connection, right?
> >
> 
> Correct, though (obviously) we're seeing the slownees remotely as well.


Hi Mike, list,

The dd and cat numbers in your email are consistent with what I get from
both my RAID5 arrays (PERC5/i controllers), with 4 and 6 15kRPM drives
(in PowerEdge 2900s).

Have you tried experimenting with stride and stripe_width ?
stride needs to be the same as whatever per disk chunk size the RAID array
was configured with (that should show up in the PERC5/E BIOS at least), and
stripe_width is stride*N with N being the number of data disks, i.e. without
parity.
I'm paraphrasing "man tune2fs", it's probably better explained there.
Those can be tuned with tune2fs (-E), although I've never done that to a
live FS, so the usual caveats about backups apply.

Sorry about the noise if that was done or discussed before, I've just read
the thread back and did find anything related to this.

Best,

Francois Cami