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