On 9/12/18 8:33 PM, lampahome wrote:
In general, we've spent more resources developing external snapshots. So
if you want the most support and the fastest response on resolving any
issues that you may encounter, external snapshots are the way to go.
So internal snapshot is hard to use than external snapshot?
Ease of use is subjective; but in general, when more of the tooling has
been optimized for external snapshots, you'll find that performing the
same task using only internal snapshots may cause longer guest
downtimes, less efficient host storage usage, or harder sequences of
commands to manage, because no one has had a priority of providing
patches to bring it up to par with external snapshots.
Is that because external snapshot is easier to roll back to any snapshot?
Again, ease of use is subjective. Actually, at the moment, if you use
libvirt, it's easier to revert to an internal snapshot (a single libvirt
command) than an external snapshot (where you have to manually rewrite
domain XML), although work is being done to get libvirt to be able to
roll back to external snapshots. But that's more a problem of libvirt
integration to qemu, and not something inherent to one or the other form
of qcow2 snapshots.
There are other things, though, such as reading the contents of an
external backing file while a guest is live, that have no counterpart
with internal snapshots (we have not yet come up with a way to export
the contents of an internal snapshot while the guest is running - you
can only do it while the image with internal snapshots is offline).
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
