linux-kernel - Re: raid io requests not parallel?

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Message-ID: <e0e4cb3e0607161557l4a24ca4by4a6d9909feb8b1b1@mail.gmail.com>
Date:	Sun, 16 Jul 2006 15:57:45 -0700
From:	"Jonathan Baccash" <jbaccash@...il.com>
To:	"Chuck Ebbert" <76306.1226@...puserve.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: raid io requests not parallel?

> Because a single read not only goes to just one disk, it is sent to
> the disk with the lowest expected seek time for that request.  This
> cuts average read time in half, on average.
>
> (See drivers/md/raid1.c::read_balance().)

Thanks Chuck! That is making some sense, although I think I'll have to
read and think about it some more before I quite understand.

> You didn't post any benchmarks showing results for single write to a
> single disk.

I didn't think I could get any repeatable results for a single write,
so I was trying to understand what is happening based on runs of
longer writes.
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