From: Chris Mason <chris.mason@oracle.com>
Subject: Re: getdents - ext4 vs btrfs performance
Date: Wed, 29 Feb 2012 09:42:44 -0500
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To: Jacek Luczak <difrost.kernel@gmail.com>
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On Wed, Feb 29, 2012 at 03:07:45PM +0100, Jacek Luczak wrote:

[ btrfs faster than ext for find and cp -a ]

> 2012/2/29 Jacek Luczak <difrost.kernel@gmail.com>:
> 
> I will try to answer the question from the broken email I've sent.
> 
> @Lukas, it was always a fresh FS on top of LVM logical volume. I've
> been cleaning cache/remounting to sync all data before (re)doing
> tests.

The next step is to get cp -a out of the picture, in this case you're
benchmarking both the read speed and the write speed (what are you
copying to btw?).

Using tar cf /dev/zero <some_dir> is one way to get a consistent picture
of the read speed.

You can confirm the theory that it is directory order causing problems
by using acp to read the data.

http://oss.oracle.com/~mason/acp/acp-0.6.tar.bz2

-chris