How to revert an external snapshot

[Dario Lesca]

I have generate an external snapshot with this command:

>  vm='win7-64'
>  
>  virsh snapshot-create-as "$vm" "$vm-snap1" "snap1
> description" \
>    --diskspec vda,file="/virt/$vm-snap1.qcow2" \
>    --disk-only --atomic 
My virsh / libvirt is the last from Fedora 21

>  [root@dodo:/virt]# virsh --version
>  1.2.9.2 
Now I have this situation:

>  [root@dodo:/virt]# ll win7-64*
>  -rw-r--r-- 1 qemu qemu 17182753280  4 mar 14.14 win7-64.qcow2
>  -rw-r--r-- 1 root root   558628864  4 mar 14.35 win7-64-snap1.qcow2
>  
>  root@dodo:/virt]# virsh snapshot-list win7-64
>   Nome                 Creation Time             Stato
>  ------------------------------------------------------------
>   win7-64-snap1        2015-03-04 14:21:15 +0100 shutoff 
But if I run the revert command this is the result:

>  [root@dodo:/virt]# virsh snapshot-revert win7-64 win7-64-snap1
>  errore: unsupported configuration: revert to external snapshot not supported yet 
There is some way to revert my vm to previous state?

Many thanks for help.

-- 
Dario Lesca
(inviato dal mio Linux Fedora 21 con Gnome 3.14)

[Cole Robinson]

On 03/04/2015 09:16 AM, Dario Lesca wrote:
>  I have generate an external snapshot with this command:
>  
> > vm='win7-64'
> >
> > virsh snapshot-create-as "$vm" "$vm-snap1" "snap1
> description" \
> >   --diskspec vda,file="/virt/$vm-snap1.qcow2" \
> >   --disk-only --atomic
>  
>  My virsh / libvirt is the last from Fedora 21
>  
> > [root@dodo:/virt]# virsh --version
> > 1.2.9.2
>  
>  Now I have this situation:
>  
> > [root@dodo:/virt]# ll win7-64*
> > -rw-r--r-- 1 qemu qemu 17182753280  4 mar 14.14 win7-64.qcow2
> > -rw-r--r-- 1 root root   558628864  4 mar 14.35 win7-64-snap1.qcow2
> >
> > root@dodo:/virt]# virsh snapshot-list win7-64
> >  Nome                 Creation Time             Stato
> > ------------------------------------------------------------
> >  win7-64-snap1        2015-03-04 14:21:15 +0100 shutoff
>  
>  But if I run the revert command this is the result:
>  
> > [root@dodo:/virt]# virsh snapshot-revert win7-64 win7-64-snap1
> > errore: unsupported configuration: revert to external snapshot not supported yet
>  
>  There is some way to revert my vm to previous state?
>  
>  Many thanks for help.
>   
You can do it by hand: Power off the VM, edit the XML to point at the desired
disk image.

However, if you point at the root file and make disk changes, the snapshot
overlay will then become invalid. So if you want to use the root contents
again, you'll need to create another overlay based on the root image, and
point your VM at that. This confusion is one of the reasons that stuff isn't
implemented in libvirt yet

- Cole

[Dario Lesca]

Il giorno mer, 04/03/2015 alle 09.49 -0500, Cole Robinson ha scritto:
>  On 03/04/2015 09:16 AM, Dario Lesca wrote:
>  > I have generate an external snapshot with this command:
>  > ...
>  > There is some way to revert my vm to previous state? 
>  You can do it by hand: Power off the VM, edit the XML to point at the
> desired
>  disk image. 
Ok, thanks Cole, I have modify the point at the disk image to original
root disk image:

        before "<source file='/virt/win7-64-snap1.qcow2'/>"
        after "<source file='/virt/win7-64.qcow2'/>"

Then I have remove the image overlay /virt/win7-64-snap1.qcow2

Now all work fine.

>  However, if you point at the root file and make disk changes, the
> snapshot
>  overlay will then become invalid. So if you want to use the root contents
>  again, you'll need to create another overlay based on the root image, and
>  point your VM at that. This confusion is one of the reasons that stuff isn't
>  implemented in libvirt yet 
But now when I list snapshot the snapshot removed is showed:

>  [root@dodo:/virt]# virsh snapshot-list win7-64
>  Nome                 Creation Time             Stato
>  ------------------------------------------------------------
>  win7-64-snap1        2015-03-04 14:21:15 +0100 shutoff 
So, I have remove the machine and recreate it and the snapshot is gone
away.

Thanks for help.

-- 
Dario Lesca
(inviato dal mio Linux Fedora 21 con Gnome 3.14)

[Cole Robinson]

On 03/04/2015 11:43 AM, Dario Lesca wrote:
>  Il giorno mer, 04/03/2015 alle 09.49 -0500, Cole Robinson ha
> scritto:
> > On 03/04/2015 09:16 AM, Dario Lesca wrote:
> >> I have generate an external snapshot with this command:
> >> ...
> >> There is some way to revert my vm to previous state?
>  
> > You can do it by hand: Power off the VM, edit the XML to point at the desired
> > disk image.
>  
>  Ok, thanks Cole, I have modify the point at the disk image to original
>  root disk image:
>  
>          before "<source file='/virt/win7-64-snap1.qcow2'/>"
>          after "<source file='/virt/win7-64.qcow2'/>"
>  
>  Then I have remove the image overlay /virt/win7-64-snap1.qcow2
>  
>  Now all work fine.
>  
> > However, if you point at the root file and make disk changes, the snapshot
> > overlay will then become invalid. So if you want to use the root contents
> > again, you'll need to create another overlay based on the root image, and
> > point your VM at that. This confusion is one of the reasons that stuff isn't
> > implemented in libvirt yet
>  
>  But now when I list snapshot the snapshot removed is showed:
>  
> > [root@dodo:/virt]# virsh snapshot-list win7-64
> > Nome                 Creation Time             Stato
> > ------------------------------------------------------------
> > win7-64-snap1        2015-03-04 14:21:15 +0100 shutoff
>  
>  So, I have remove the machine and recreate it and the snapshot is gone
>  away.
>   
For that last bit, you should be able to do:

sudo virsh snapshot-delete --metadata $snapshot-name

- Cole

[Dario Lesca]

Il giorno mer, 04/03/2015 alle 12.01 -0500, Cole Robinson ha scritto:
>  For that last bit, you should be able to do:
>  
>  sudo virsh snapshot-delete --metadata $snapshot-name 
Thanks Cole, and thanks also to Kashyap for the useful link.

But, for me, traslate this info into a procedure (shell script) for do
an hot backup/restore of my virtual machine is difficult.

I intend use external snapshot for transfer, without poweroff, a guest
from host to bk-host.

With external snapshot, my idea was to transfer the base image from host
to bk-host and, at the end of copy base image, to remove the snapshot on
host.

It's possible to do that or something like this?
there is already some scripts?

Thanks for your help ... and great work.
-- 
Dario Lesca
(inviato dal mio Linux Fedora 21 con Gnome 3.14)

[Eric Blake]

On 03/09/2015 02:40 AM, Dario Lesca wrote:
>  Il giorno mer, 04/03/2015 alle 12.01 -0500, Cole Robinson ha
> scritto:
> > For that last bit, you should be able to do:
> >
> > sudo virsh snapshot-delete --metadata $snapshot-name
>  
>  Thanks Cole, and thanks also to Kashyap for the useful link.
>  
>  But, for me, traslate this info into a procedure (shell script) for do
>  an hot backup/restore of my virtual machine is difficult.
>  
>  I intend use external snapshot for transfer, without poweroff, a guest
>  from host to bk-host.
>  
>  With external snapshot, my idea was to transfer the base image from host
>  to bk-host and, at the end of copy base image, to remove the snapshot on
>  host.
>  
>  It's possible to do that or something like this? 
Yes.  It sounds like this will do it:

# Create the external snapshot
virsh snapshot-create $dom --no-metadata --disk-only
# Copy the base image to bk-host, for an appropriate $copy
"$copy" host... bk-host...
# Commit the temporary qcow2 snapshot wrapper back into the main disk
foreach disk in $dom:
  virsh blockcommit $dom $disk --active --shallow --verbose --pivot

and now your host is back to executing with the original file as active,
with no notion that a backup was taken in the meantime, and with guest
downtime limited to millisecond or less ranges.  The backup image now
stored on bk-host is not consistent (that is, libvirt still needs to add
support for a 'snapshot-create --quiesce' flag); if that matters, you
can use this longer sequence (assuming you have new enough libvirt):

virsh domfsfreeze $dom
virsh snapshot-create $dom --no-metadata --disk-only
virsh domfsthaw $dom
"$copy" host... bk-host...
etc.

>  there is already some scripts? 
I don't know if anyone else has tried to script it, but I haven't.

>  
>  Thanks for your help ... and great work.
>   
-- 
Eric Blake   eblake redhat com    [phone]
Libvirt virtualization library http://libvirt.org

[Kashyap Chamarthy]

On Mon, Mar 09, 2015 at 10:37:55AM -0600, Eric Blake wrote:
>  On 03/09/2015 02:40 AM, Dario Lesca wrote:
>  > Il giorno mer, 04/03/2015 alle 12.01 -0500, Cole Robinson ha scritto:
>  >> For that last bit, you should be able to do:
>  >>
>  >> sudo virsh snapshot-delete --metadata $snapshot-name
>  > 
>  > Thanks Cole, and thanks also to Kashyap for the useful link.
>  > 
>  > But, for me, traslate this info into a procedure (shell script) for do
>  > an hot backup/restore of my virtual machine is difficult.
>  > 
>  > I intend use external snapshot for transfer, without poweroff, a guest
>  > from host to bk-host.
>  > 
>  > With external snapshot, my idea was to transfer the base image from host
>  > to bk-host and, at the end of copy base image, to remove the snapshot on
>  > host.
>  > 
>  > It's possible to do that or something like this?
>  
>  Yes.  It sounds like this will do it:
>  
>  # Create the external snapshot
>  virsh snapshot-create $dom --no-metadata --disk-only
>  # Copy the base image to bk-host, for an appropriate $copy
>  "$copy" host... bk-host...
>  # Commit the temporary qcow2 snapshot wrapper back into the main disk
>  foreach disk in $dom:
>    virsh blockcommit $dom $disk --active --shallow --verbose --pivot 
The above procedure (derived from mailing lists conversation with Eric)
is documented here with a little more commentary:

    http://wiki.libvirt.org/page/Live-disk-backup-with-active-blockcommit

--
/kashyap

>  and now your host is back to executing with the original file as
> active,
>  with no notion that a backup was taken in the meantime, and with guest
>  downtime limited to millisecond or less ranges.  The backup image now
>  stored on bk-host is not consistent (that is, libvirt still needs to add
>  support for a 'snapshot-create --quiesce' flag); if that matters, you
>  can use this longer sequence (assuming you have new enough libvirt):
>  
>  virsh domfsfreeze $dom
>  virsh snapshot-create $dom --no-metadata --disk-only
>  virsh domfsthaw $dom 
Thanks for the 'domfsthaw' reminder, I forgot about it.

>  "$copy" host... bk-host...
>  etc.
>  
>  > there is already some scripts?
>  
>  I don't know if anyone else has tried to script it, but I haven't.

[Kashyap Chamarthy]

On Wed, Mar 04, 2015 at 05:43:30PM +0100, Dario Lesca wrote:
>  Il giorno mer, 04/03/2015 alle 09.49 -0500, Cole Robinson ha
> scritto:
>  > On 03/04/2015 09:16 AM, Dario Lesca wrote:
>  > > I have generate an external snapshot with this command:
>  > > ...
>  > > There is some way to revert my vm to previous state?
>  
>  > You can do it by hand: Power off the VM, edit the XML to point at the desired
>  > disk image.
>  
>  Ok, thanks Cole, I have modify the point at the disk image to original
>  root disk image:
>  
>          before "<source file='/virt/win7-64-snap1.qcow2'/>"
>          after "<source file='/virt/win7-64.qcow2'/>"
>  
>  Then I have remove the image overlay /virt/win7-64-snap1.qcow2
>  
>  Now all work fine.
>  
>  > However, if you point at the root file and make disk changes, the snapshot
>  > overlay will then become invalid. So if you want to use the root contents
>  > again, you'll need to create another overlay based on the root image, and
>  > point your VM at that. This confusion is one of the reasons that stuff isn't
>  > implemented in libvirt yet
>  
>  But now when I list snapshot the snapshot removed is showed:
>  
>  > [root@dodo:/virt]# virsh snapshot-list win7-64
>  > Nome                 Creation Time             Stato
>  > ------------------------------------------------------------
>  > win7-64-snap1        2015-03-04 14:21:15 +0100 shutoff
>  
>  So, I have remove the machine and recreate it and the snapshot is gone
>  away.
>  
>  Thanks for help. 
Along with what Cole said, here is some more explanation
into revert/deletion of external snapshots (written by Eric Blake)

   
http://wiki.libvirt.org/page/I_created_an_external_snapshot,_but_libvirt_...

And, also look up the archives of 'libvirt-users' mailing list for
similar questions -- there's lot of useful info there too.

-- 
/kashyap