From: Ted Ts'o <tytso@mit.edu>
Subject: Re: getdents - ext4 vs btrfs performance
Date: Thu, 1 Mar 2012 13:42:48 -0500
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Cc: Chris Mason <chris.mason@oracle.com>,
	Hillf Danton <dhillf@gmail.com>, linux-ext4@vger.kernel.org,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, linux-btrfs@vger.kernel.org,
	lczerner@redhat.com
To: Jacek Luczak <difrost.kernel@gmail.com>
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On Thu, Mar 01, 2012 at 03:43:41PM +0100, Jacek Luczak wrote:
> 
> Yep, ext4 is close to my wife's closet.
> 

Were all of the file systems freshly laid down, or was this an aged
ext4 file system?

Also you should beware that if you have a workload which is heavy
parallel I/O, with lots of random, read/write accesses to small files,
a benchmark using tar might not be representative of what you will see
in production --- different file systems have different strengths and
weaknesses --- and the fact that ext3/ext4's readdir() returns inodes
in a non-optimal order for stat(2) or unlink(2) or file copy in the
cold cache case may not matter as much as you think in a build server.
(i.e., the directories that do need to be searched will probably be
serviced out of the dentry cache, etc.)

Regards,

						- Ted