Re: [libvirt-users] Pivot without copy
On 05/19/2015 02:41 PM, Mathew Moon wrote:
Hi Eric,
[please don't top-post on technical lists]
Thanks for the info. I see the value in this, but it isn't quite what I was
looking for. Basically what I want to do is to switch between snapshots
quickly. For instance, I am currently working on designing a HA SQL
implementation with failover. So right now I have 5 VM's running postgresql
as a replication group. I am trying a lot of different things and often
have to take a snapshot of all 5 VM's, do some work, and then to revert to
the previous snapshot I have to:
1. kill the VM
2. edit the VM's config
3. start the VM
What I would like is to be able to "pivot" the "current" image to be
the
previous snapshot (in most cases). I understand that if this were possible
then there would be applications crash because something on disk doesn't
jive with what is in memory, but I am ok with that, I just want to get my
databases back to "square one" quickly after something in the procedure I
am working on foo bar's my db and it is replicated to 4 other nodes.
That sounds more like snapshot-revert, except that we haven't wired up
snapshot revert to work with external snapshots yet. You can experiment
with internal snapshots, but those have more guest downtime than
external snapshots. Would you like to help write the patches for
reverting to external snapshots?
Any insights on how this could be accomplished using libvirt without
rebooting?
Snapshot revert will roll back both the disk state and the memory state
to an earlier point in guest time. But if you don't care about guest
memory, you could possibly hot-unplug the disk that has the state you no
longer want, then hot-plug the updated disk that does have what you
want. If your guest can handle storage going away and then being
plugged in, then that is just as effective as anything that snapshots
would do at rolling back to a known disk state.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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