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Re: [Xen-users] Consistent VM image backups

To: Mike Sun <msun@xxxxxxxxxx>
Subject: Re: [Xen-users] Consistent VM image backups
From: "Fajar A. Nugraha" <list@xxxxxxxxx>
Date: Fri, 28 Jan 2011 09:02:08 +0700
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On Fri, Jan 28, 2011 at 5:00 AM, Mike Sun <msun@xxxxxxxxxx> wrote:
> Hi,
> 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?

There are problems with loopback driver, but I don't think it's one of them.

>  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?

See "Advantages" on http://wiki.xensource.com/xenwiki/blktap


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