[libvirt-users] backup procedure using blockcopy

[Thomas Stein]

Am 02.07.13 15:42, schrieb Eric Blake:
> On 07/02/2013 06:55 AM, Thomas Stein wrote:
>> 
>>>   virsh dumpxml --security-info dom > dom.xml
>>>   virsh undefine dom
>> 
>> Hello.
>> 
>> Someone was talking about this (undefining the VM) would not be
>> neccessary anymore when qemu-1.5 has been released. Is that true?
> 
> Undefining the VM will not be necessary after two things happen:
> 1. qemu supports persistent bitmaps (which missed 1.5, and I'm not even
> sure if Paolo plans on getting it in before 1.6)
> 2. libvirt has code added to use persistent bitmaps
> 
> so unfortunately, you'll still have to use undefining for a bit longer.
> 
> Meanwhile, qemu 1.6 is adding a new block-backup command that is nicer
> than the current blockcopy (it does not require a persistent bitmap, and
> takes the snapshot at the point in time where it is started, not where
> it is ended); I'm also trying to figure out what API additions are
> needed to libvirt to expose that capability as an alternative.

Okay, understood.

>> 
>>>   virsh blockcopy dom vda /path/to/backup-vda
>>>   polling loop - check periodically until 'virsh blockjob dom vda'
>>>   shows 100% completion
>>>   virsh suspend dom
>>>   virsh save dom /path/to/memory-backup --running
>> 
>> This does not work for me.
>> 
>> hn ~ # virsh blockjob gentoo-template vda
>> Block Copy: [100 %]
>> 
>> hn ~ # virsh save gentoo-template
>> /opt/virt-backup-blockcopy/gentoo-template/gentoo-template-memory-backup
>> --running
>> error: Failed to save domain gentoo-template to
>> /opt/virt-backup-blockcopy/gentoo-template/gentoo-template-memory-backup
>> error: Requested operation is not valid: domain has an active block job
>> 
>> Obviously i can not save while the blockjob is running.
> 
> Oh dear.  That's what I get for trying to write steps without actually
> testing them :(
> 
> Try this modification (again untested, but at least doesn't have a block
> job running during the save attempt):
> 
>    virsh dumpxml --security-info dom > dom.xml
>    virsh undefine dom
>    virsh blockcopy dom vda /path/to/backup-vda
>    polling loop - check periodically until 'virsh blockjob dom vda'
>      shows 100% completion
>    virsh suspend dom
>    virsh blockjob dom vda --abort
>    virsh save dom /path/to/memory-backup --running
>    virsh resume dom
>    virsh define dom.xml

Much better but still a problem.

virsh suspend gentoo-template
Domain gentoo-template suspended

virsh blockjob gentoo-template vda --abort

virsh save gentoo-template
/opt/virt-backup-blockcopy/gentoo-template/gentoo-template-memory

Domain gentoo-template saved to
/opt/virt-backup-blockcopy/gentoo-template/gentoo-template-memory

virsh resume gentoo-template
error: failed to get domain 'gentoo-template'
error: Domain not found: no domain with matching name 'gentoo-template'

> Basically, swap the 'blockjob --abort' and 'save' steps to take place in
> the opposite order.  Since the guest is paused, there should be no
> difference in the bits that get saved, and the swapped order should get
> around the annoying code restrictions.

I think i have to use "start" instead of "resume" although i don't
understand this behaviour. Maybe i have to define the VM first? Is
"virsh save dom" shutting down the VM?

Thank you very much Eric.

t.