From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <4D6F6D8D.6010001@redhat.com>
Date: Thu, 03 Mar 2011 10:29:33 +0000
From: "Bryn M. Reeves" <bmr@redhat.com>
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References: <4D6EA3EF.1070401@bartk.us>
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Subject: Re: [linux-lvm] Tracing IO requests?
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To: LVM general discussion and development <linux-lvm@redhat.com>
Cc: Bart Kus <me@bartk.us>

On 03/02/2011 08:09 PM, Bart Kus wrote:
> Hello,
> 
> I have the following setup:
> 
> md_RAID6(10x2TB) -> LVM2 -> cryptsetup -> XFS
> 
> When copying data onto the target XFS, I notice a large number of READs 
> occurring on the physical hard drives.  Is there any way of monitoring 
> what might be causing these read ops?

The blktrace command is extremely useful for this kind of I/O tracing. I've used
it numerous times to figure out where I/O is originating and also how it's
making its way through layers of stacked devices.

There's a conference talk overview here from a few years ago:

http://www.gelato.org/pdf/apr2006/gelato_ICE06apr_blktrace_brunelle_hp.pdf

And also a user's guide:

http://www.cse.unsw.edu.au/~aaronc/iosched/doc/blktrace.html
http://pdfedit.petricek.net/bt/file_download.php?file_id=17&type=bug

Regards,
Bryn.