[libvirt-users] Live snapshots of a single block device

[Eric Blake]

On 05/23/2014 12:16 PM, Andrew Martin wrote:

>> --quiesce requires the guest to be running to work, while --memspec
>> forceably stops the guest (the migration algorithm must pause, even if
>> --live minimizes the pause to a fraction of a second).
> Would calling snapshot-create-as with --disk-only and --quiese still succeed
> on a VM that is stopped (since the disk would already be consistent, it would
> just call "qemu-img create")?

For an offline guest, --disk-only makes no difference (there is no
memory to worry about); and you are correct that the disk is consistent
(assuming the OS has a clean shutdown before going offline).  Yes,
calling 'qemu-img create' is basically what libvirt does for an offline
external snapshot.

However, a paused/stopped guest cannot respond to a quiesce request (the
guest agent only works if the guest is running), so your attempt to use
--quiesce would fail; you'd have to omit the parameter if the guest is
stopped.

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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 604 bytes
Desc: OpenPGP digital signature
URL: <http://listman.redhat.com/archives/libvirt-users/attachments/20140523/2665a419/attachment.sig>