----- Original Message -----
From: "Eric Blake" <eblake@redhat.com> To: "Andrew Martin" <amartin@xes-inc.com> Cc: libvirt-users@redhat.com Sent: Friday, May 23, 2014 7:30:44 PM Subject: Re: [libvirt-users] Live snapshots of a single block device
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.
Okay, that makes sense to me. Thanks for the clarification! Andrew