From: Andreas Dilger <adilger@clusterfs.com>
To: Jan Kara <jack@suse.cz>
Cc: David Chinner <dgc@sgi.com>,
linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org
Subject: Re: [RFC] Defragmentation interface
Date: Sat, 4 Nov 2006 03:22:16 +0800 [thread overview]
Message-ID: <20061103192216.GA5252@schatzie.adilger.int> (raw)
In-Reply-To: <20061103143030.GB17306@atrey.karlin.mff.cuni.cz>
On Nov 03, 2006 15:30 +0100, Jan Kara wrote:
> > - stripe unit and stripe width need to be exposed so defrag too
> > can make correct placement decisions.
> fs-specific thing...
I think this is not just XFS-specific. It is very desirable to align
large IO to the RAID stripe so that if you write stripe_width bytes
you don't do 2 expensive read-modify-write steps, but rather a single
write operation. Also RAID controllers have (large) internal cache
"lines" and having aligned reads can help noticably, and also if array
is doing RAID parity checking to avoid overhead of doing this for two
stripes instead of one.
Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.
next prev parent reply other threads:[~2006-11-03 19:22 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-11-02 14:39 [RFC] Defragmentation interface Jan Kara
2006-11-02 22:59 ` David Chinner
2006-11-03 14:30 ` Jan Kara
2006-11-03 19:22 ` Andreas Dilger [this message]
2006-11-03 19:38 ` Jan Kara
2006-11-06 2:54 ` David Chinner
2006-11-06 17:44 ` Jan Kara
2006-11-07 3:03 ` David Chinner
2006-11-03 14:50 ` Dave Kleikamp
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