On Tue, Apr 28, 2009 at 01:30:59PM -0500, Kevin Grittner wrote:
> Craig James <craig_james@emolecules.com> wrote:
>
> > After a reading various articles, I thought that "noop" was the
> > right choice when you're using a battery-backed RAID controller.
> > The RAID controller is going to cache all data and reschedule the
> > writes anyway, so the kernal schedule is irrelevant at best, and can
> > slow things down.
>
> Wouldn't that depend on the relative sizes of those caches? In a
> not-so-hypothetical example, we have machines with 120 GB OS cache,
> and 256 MB BBU RAID controller cache. We seem to benefit from
> elevator=deadline at the OS level.
>
> -Kevin
>
This was my understanding as well. If your RAID controller had a
lot of well managed cache, then the noop scheduler was a win. Less
performant RAID controllers benefit from teh deadline scheduler.
Cheers,
Ken
