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[Xen-devel] xen DomU image on RAID5 + XFS causes issues with tap:aio

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Subject: [Xen-devel] xen DomU image on RAID5 + XFS causes issues with tap:aio
From: Steven Haigh <netwiz@xxxxxxxxx>
Date: Tue, 27 Apr 2010 06:07:09 +1000
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Hi all,

Firstly, I'm not subscribed to this list so please CC me into replies.

Upon bashing my head against a wall trying to get Xen working on my new
hardware I came across an interesting discovery. Every install using
virt-install was failing and I could only use the file: access method for
my DomUs. Every time I tries to use tap:aio the guest would error on boot
saying it couldn't find the root partition.

My system is as follows:
OS: CentOS 5.4
Xen: 3.0.3-94.el5_4.3
/ = 2 x 80Gb HDDs, dmraid1, ext3
/mnt/raid = 3 x 1Tb HDDs, dmraid5, xfs

On whim, I moved the DomU images from /mnt/raid/vm-images to /vm-images
and instantly tap:aio worked again.

This brings me to my question:

Why would tap:aio fail when the images are on an XFS/RAID5 filesystem but
work correctly when on a RAID1/ext3 filesystem?

To me, this seems like a bug.

Steven Haigh
Email: netwiz@xxxxxxxxx
Web: http://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897
Fax: (03) 8338 0299

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