[vbox-dev] VB backup

Sergey Malykhin sergey.malykhin at gmail.com
Tue Mar 30 02:51:00 PDT 2010


Thanks, Klaus.

I understand that it's not 100% safe way :)

Thanks again

30 марта 2010 г. 16:43 пользователь Klaus Espenlaub <Klaus.Espenlaub at sun.com
> написал:

> Sergey Malykhin wrote:
>
>> Thanks, Nikolay,
>>
>> I meant that I hacked kernel a little to get information about file, data
>> buffer, buffer size and offset in file. And it's ok. I'm only not sure that
>> I'll have working backup if do it while VB is running. I understand that the
>> best solution - suspend VB and copy, but it's less interestin, because I'll
>> have pauses in VB work.
>>
>
> Sorry to sound a little annoyed, but I really don't understand why adding a
> little virtualization makes people think they're looking at something they
> never did before.
>
> Creating a copy of the VDI file (no matter how smart is it done by
> intercepting file writes and what not) is just like creating a sector-based
> copy of a hard disk without knowledge of the running guest OS. Without
> taking special measures (for most OSes I wouldn't know what to do actually)
> there cannot be any guarantee that the resulting copy is consistent. Even
> pausing a VM will not fundamentally change this, because the guest OS could
> have unwritten changes in its filesystem cache, i.e. in RAM. It'll
> frequently work without noticeable corruption, but it remains a "keep
> fingers crossed" solution.
>
> The only safe ways to create backups are those which the guest OS is aware
> of (file-based or guest OS based snapshotting like Nikolay suggested), or
> completely shut down the guest OS. Using mechanisms like saving state in
> VirtualBox would require backing up the VM state file as well.
>
> Klaus
>
>  Sergey
>>
>> 2010/3/30 Nikolay Igotti <Nikolay.Igotti at sun.com <mailto:
>> Nikolay.Igotti at sun.com>>
>>
>>
>>     Hi Sergey,
>>
>>    Not sure what you mean by "I'm controlling write function to vdi
>>    file from kernel", but in general it's possible to use FS's (such as
>>    ZFS) snapshotting capability to take snapshots of live VMs image.
>>    OTOH to be 100% safe, I would pause VM, flush OS write buffers with
>>    'sync', and then copy underlying .vdi.
>>    If you assume image to change insignificantly, maybe it would make
>>    sense to take snapshot once image stabilized, and only backup
>>    differences.
>>
>>    Hope that'll help,
>>    Nikolay
>>
>>
>>
>>    Sergey Malykhin пишет:
>>
>>        Hello,
>>
>>        I have VB running and want to make backup for vdi file. But I
>>        only need to have changed sectors. I'm controlling write
>>        function to vdi file from kernel. Can you please answer is it
>>        enough just copy it while VM is running or I need to suspend it?
>>
>>        TIA
>>
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>>
>>
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>
>
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> Dr. Klaus Espenlaub
> Sun Microsystems GmbH
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