Re: [Xen-devel] A Problem with Page Cache in Xen

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2012-01-30 at 08:11 +0000, hxkhust wrote:
> Hi,
>  
> Recently I'm dong some reserch on xen and encounter a problem that I
> cannot solve temporarily.I need your help very much and the following
> is the question I would like to ask:
> On a physical machine with xen virtualization platform installed ,VM
> A,VM B are VM C's virtual disks are all image files,among which VM A
> and VM B's virtual disks are QCOW2 format and VM C's disk is RAW
> format. And VM A and VM B's virtual disk image files are based on VM
> C's virtual disk image file.Now these three VMs are running on the
> same physical machine with xen installed.

This is an invalid/dangerous configuration. You can't really safely
write to the backing file (C's raw disk) while there are active users (A
and B's qcow2 images) of it. Imagine e.g. that all three change the same
bit of filesystem metadata in different ways...

Ian.



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