Re: Best choice for copy/clone/snapshot

[Avi Kivity <avi@redhat.com>]

Ross Boylan wrote:
> Thanks for all the info.  I have one follow up.
> On Wed, 2009-05-13 at 10:07 +0300, Avi Kivity wrote:
>   
>>> As I install software onto a system I want to preserve its
>>>       
>> state--just
>>     
>>> the disk state---at various points so I can go back.  What is the
>>>       
>> best
>>     
>>> way to do this?
>>>   
>>>       
>> LVM snapshots.  Read up on the 'lvcreate -s' command and option.
>>     
> I may have been unclear.  I meant as I install software on the VM.
> Since some of them are running Windows, they can't do LVM.  I am running
> LVM on my host Linux system.
>
> Or are you suggesting that I put the image files on a snapshottable
> partition?  Over time the snapshot seems likely to accumulate a lot of
> original sectors that don't involve the disk image I care about.
>
> Or do you mean I should back each virtual disk with an LVM volume?  That
> does seem cleaner; I've just been following the docs and they use
> regular files.  They say I can't just use a raw partition, but maybe
> kvm-img -f qcow2 /dev/MyVolumeGroup/Volume10 ?
>   

You can certainly use a raw partition, for example

  qemu-system-x86_64 -drive file=/dev/vg0/guest1,cache=none

> Does that give better performance?  

That is the highest performing option, especially with cache=none.

> The one drawback I see is that I'd
> have to really take the space I wanted, rather than having it only
> notionally reserved for a file.  

Yes, that's a drawback, and there's currently no way around it.

> I'm not sure how growing the logical
> volume would interact with qcow...
>   

It should work, but I wouldn't recommend it.

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