linux-kernel - Re: RAID performance / tuning?

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Message-ID: <159a870e0904021236m6ef4444eh66ec42e34aa24291@mail.gmail.com>
Date:	Thu, 2 Apr 2009 16:36:28 -0300
From:	Tiago Freire <tiago.freire@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: RAID performance / tuning?

I would like to believe this is not the case with Intel ICH9R...

Anyway, I want to make sure I have done everything possible to speed
up my 6-disk RAID.
Scheduling concurernt IO may not have a best single solution, I know,
but is the kernel 'perfect' in the sense of giving the RAID / SATA
subsystems all the cpu cycles it needs to perform best (with the
lowest possible latency)? Or do we have some knobs to tune the kernel?

On Thu, Apr 2, 2009 at 2:41 PM,  <david.hagood@...il.com> wrote:
>
>> Why is it that software RAID on current systems still gets less
>> performance than hardware counterparts?
>
> Part of it can be crappy disk interfaces: I was running software raid with
> 2 SATA-SIL cards, and would frequently be disk-bound with the CPU still
> largely idle.
>
> The cards were incapable of talking to more than one drive at a time. They
> didn't support command queuing on the drives.
>
> As a result, the system would set up a stripe, queue up the writes, then
> have to wait as each write for EACH DISK in the 7 disk array was carried
> out.
>
> On a good hardware RAID controller, the disks can be written in parallel,
> and the controller will support command queuing - so disk writes can be
> run in parallel, and the writes themselves can be better optimized by the
> disks.
>
>
>

-- 
-----
Tiago Mikhael Pastorello Freire a.k.a. Brazilian Joe
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