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

[Andrew Martin]

----- Original Message -----
> From: "Eric Blake" <eblake at redhat.com>
> To: "Andrew Martin" <amartin at xes-inc.com>
> Cc: libvirt-users at 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