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Re: [Qemu-devel] Using the one disk image file on 2 virtual machines at
From: |
John Snow |
Subject: |
Re: [Qemu-devel] Using the one disk image file on 2 virtual machines at the same time |
Date: |
Wed, 29 Jul 2015 13:46:38 -0400 |
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Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
On 07/29/2015 01:29 PM, Manjong Han wrote:
> Thanks, Stefan.
>
> 2015-07-29 17:46 GMT+09:00 Stefan Hajnoczi <address@hidden>:
>>
>> You should probably use qcow2 backing files instead:
>>
>> 10G.qcow2 <-- vm001.qcow2
>> ^-- vm002.qcow2
>>
>> The command to create these files is:
>>
>> qemu-img create -f qcow2 -o backing_file=10G.qcow2 vm001.qcow2.
>>
>> Both VMs share the data in 10G.qcow2. All writes go to vm001.qcow2 or
>> vm002.qcow2, respectively, so they don't corrupt each other.
>>
>
> I tried to create a backing files, using the commands which you told.
>
> $ qemu-img create -f qcow2 -o backing_file=10G.qcow2 vm001.qcow2
> $ qemu-img create -f qcow2 -o backing_file=10G.qcow2 vm002.qcow2
>
> And, I used these backing files on each virtual machines.
> But, new files weren't written on original disk image(10G.qcow2)..
> The backing files were working each other.
>
>> Standard file systems (ext4, xfs) and volume managers (LVM) are not
>> cluster-aware by default. They must only be accessed from one machine
>> at a time. Otherwise you risk data corruption.
>>
>
> I think that I must probably use a shared file system like NFS..
>
Yes, any files written using the backing files like outlined above will
put new files in the overlays (e.g. vm001.qcow2 or vm002.qcow2) and NOT
into the backing file (10G.qcow2)
this is a safe way to share a base image for an OS, but it's not a
method of accomplishing a concurrent fileshare.
You'll want to configure an NFS or CIFS share (etc) in the base image
and then allow the multiple VMs to utilize that share.
--js