On Tue, Apr 28, 2009 at 12:40 PM, Kenneth Marshall <ktm@rice.edu> wrote:
> 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.
I have an Areca 1680ix with 512M cache on a machine with 32Gig ram and
I get slightly better performance and lower load factors from deadline
than from noop, but it's not by much.
