linux-kernel - Re: [Xen-devel] domU is causing misaligned disk writes

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Message-ID: <20100420200004.GQ5660@tracyreed.org>
Date:	Tue, 20 Apr 2010 13:00:04 -0700
From:	Tracy Reed <treed@...raviolet.org>
To:	Pasi Kärkkäinen <pasik@....fi>
Cc:	xen-devel@...ts.xensource.com,
	Aoetools-discuss@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] domU is causing misaligned disk writes

On Tue, Apr 20, 2010 at 11:49:55AM +0300, Pasi Kärkkäinen spake thusly:
> Are you using filesystems on normal partitions, or LVM in the domU? 
> I'm pretty sure this is a domU partitioning problem.

Also: What changes in the view of the partitioning between domU and
dom0? Wouldn't a partitioning error manifest itself in tests in the
dom0 as well as in the domU?

BTW: The dd from the last time in my last email finally finished:

# dd if=/dev/zero of=/dev/xvdg1 bs=4096 count=3000000
3000000+0 records in
3000000+0 records out
12288000000 bytes (12 GB) copied, 734.714 seconds, 16.7 MB/s

If I run that very same dd as above (the last test in my previous
email) with the same partition setup again but this time from the
dom0:

# dd if=/dev/zero of=/dev/etherd/e6.1 bs=4096 count=3000000
3000000+0 records in
3000000+0 records out
12288000000 bytes (12 GB) copied, 107.352 seconds, 114 MB/s

# /sbin/sfdisk -d /dev/etherd/e6.1 
# partition table of /dev/etherd/e6.1
unit: sectors

/dev/etherd/e6.1p1 : start=       64, size=566226926, Id=83
/dev/etherd/e6.1p2 : start=        0, size=        0, Id= 0
/dev/etherd/e6.1p3 : start=        0, size=        0, Id= 0
/dev/etherd/e6.1p4 : start=        0, size=        0, Id= 0

Device:         rrqm/s   wrqm/s   r/s   w/s    rkB/s    wkB/s avgrq-sz
avgqu-sz   await  svctm  %util
sda               0.00 17350.80  0.60 275.60    22.40 72540.00
525.43    97.94  344.01   3.62 100.02
sdb               0.00 17374.80  1.20 256.00    28.00 74848.00
582.24   136.20  527.72   3.89 100.02

72MB/s and 74MB/s per disk in the stripe. Nice. Wish I could get that in a domU!

-- 
Tracy Reed
http://tracyreed.org

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