libvirt users - Jul 2013 - Re: backup procedure using blockcopy

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.

On 07/02/2013 08:19 AM, Thomas Stein wrote:
>> 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
Good through here.
>>    virsh resume dom
>>    virsh define dom.xml
> 
> 
> virsh resume gentoo-template
> error: failed to get domain 'gentoo-template'
> error: Domain not found: no domain with matching name
'gentoo-template'
Aha - then 'virsh resume dom' is not correct; we merely need 'virsh
restore /path/to/memory-backup' which should load from the memory save
file and start it running again (since we saved it with --running in the
first place).
> 
> 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?
'virsh start' would resume a managed-save guest, but we aren't using
managed save.  You want 'restore'.  And yes, 'virsh save' shuts
down the
guest (we might enhance it in the future to leave the guest running
after the save image has completed, now that we have a use case for
doing so, but that won't help you with current versions of libvirt).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Am 02.07.13 17:43, schrieb Eric Blake:
> On 07/02/2013 08:19 AM, Thomas Stein wrote:
>>> 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
> 
> Good through here.
> 
>>>    virsh resume dom
>>>    virsh define dom.xml
>> 
> 
>> 
>> virsh resume gentoo-template
>> error: failed to get domain 'gentoo-template'
>> error: Domain not found: no domain with matching name
'gentoo-template'
> 
> Aha - then 'virsh resume dom' is not correct; we merely need
'virsh
> restore /path/to/memory-backup' which should load from the memory save
> file and start it running again (since we saved it with --running in the
> first place).
Yes. This works. So for now my backup looks like this:

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 restore /path/to/memory-backup
virsh resume dom
virsh define dom

Thank you again Eric. I'm quite happy with that solution.

Thomas