linux-ext4 - Re: getdents - ext4 vs btrfs performance

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Message-ID: <20120301184248.GC32588@thunk.org>
Date:	Thu, 1 Mar 2012 13:42:48 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Jacek Luczak <difrost.kernel@...il.com>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Hillf Danton <dhillf@...il.com>, linux-ext4@...r.kernel.org,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-btrfs@...r.kernel.org,
	lczerner@...hat.com
Subject: Re: getdents - ext4 vs btrfs performance

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
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