linux-ext4 - Re: Question on block group allocation

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Message-ID: <20090427104221.GB9059@mit.edu>
Date:	Mon, 27 Apr 2009 06:42:21 -0400
From:	Theodore Tso <tytso@....edu>
To:	Curt Wohlgemuth <curtw@...gle.com>
Cc:	Andreas Dilger <adilger@....com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Question on block group allocation

On Sun, Apr 26, 2009 at 11:29:39PM -0600, Curt Wohlgemuth wrote:
> 
> The random read throughput on the 10GB file went from ~16 MB/s to ~22
> MB/s after Andreas' patch; the total fragmentation of the file was
> much lower than before his patch.
> 
> However, the number of extents went up by quite a bit (I don't have
> the debugfs output in front of me at the moment, sorry).  It seemed
> that no extent crossed a block group; I didn't have time to see if
> Andreas' patch disabled flex BGs or not, as to what was going on.

Try running e2fsck with the "-E fragcheck" option, and then capture
e2fsck's stdout.  It will help with the grunt work of doing the
analysis, in terms of displaying the details of all of the files which
are discontiguous.

						- Ted
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