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

[hxkhust <hxkhust@xxxxxxx>]

In the situation I consider here,the VM C won't be running again after it's set up.The existence of VM C is  only for VM A and VM B's running.If VM A or VM B change some blocks in its file system,the change will only be stored in its own virtual disk image whose format is QCOW2.That's meaning which I would like to express.However I cannot find the solution to my problem temporarily.Your further suggest is helpful for me.

At 2012-01-31 00:18:58,"Ian Campbell" <Ian.Campbell@xxxxxxxxxx> wrote:
>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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