linux-ext4 - Re: [RFC] store RAID stride in superblock

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Message-Id: <1178962364.20145.99.camel@eric-laptop>
Date:	Sat, 12 May 2007 02:32:44 -0700
From:	Eric <erpo41@...il.com>
To:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [RFC] store RAID stride in superblock

On Sat, 2007-05-12 at 12:33 +0400, Alex Tomas wrote:
> > In the unlikely event that the RAID stride were to change, I think the
> > autodetect-each-time method would be superior to the store-in-superblock
> > method.
> 
> true, but in some cases (hardware raid, SAN, etc) there is no easy way
> to learn that other than asking user.

That hadn't occurred to me. Perhaps the filesystem driver or mkfs could
probe for the stride in those cases? If the code asks for, say, 10MiB of
data from the block device and it gets back sectors that are spaced
128KiB apart before it gets the rest of the data, it can make an
intelligent guess about the stride.

I wonder what penalties would come from a bad guess due to a cache in
between the block device driver and the disk platters, or other load on
a SAN...

Eric

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