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[Xen-users] Consistent VM image backups

To: XEN Mailing List <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-users] Consistent VM image backups
From: Mike Sun <msun@xxxxxxxxxx>
Date: Thu, 27 Jan 2011 17:00:55 -0500
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If a VM is using a file backed disk through the means of a loop-back
device, is there a risk that the image file may not be consistent
given that dom0 which does the loop-back mount of the file may be
caching certain portions of that file?  For example, if on dom0 I have
a disk.img and I configure my domU to use that file as it's virtual
disk through a loop back device driver, while domU is running or even
paused, it's virtual disk may not be completely synced with the actual
image file backing that disk, right?  Does the use of the blktap
driver eliminate this problem?

My overall goal is to be able to take periodic, incremental snapshots
of the VM's disks.  I thought about using LVM2's snapshotting
functionality as well as ZFS.  Any recommendations as to the best way
to take incremental snapshots of a file backed virtual disk?


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