Sometime soon I'm going to need to migrate a few hundred VMs from one
(nova-network-using) cloud to a newer (neutron-having) cloud. Google
searches for suggestions about inter-cloud migration get me a whole lot
of pages that suggest should I do this by taking snapshots in the old
cloud and importing those snapshots into Glance on the new cloud.
Doesn't that migration path result in a massive increase in storage
needs in the new cloud? Right now I have a small number of shared base
images and a large number of copy-on-write instances. If I create
snapshots for each VM, won't my new Glance server need to have storage
capacity equal to 100% of the expanded size of every one of my instances?
Or, alternatively, maybe people using this method are purging the
imported Glance images after the migration -- if that's so, then they
can't be using copy-on-write, so that would drastically increase my
storage needs on the compute side instead.
Am I missing something? Does glance support e.g.
images-backed-by-other-images so that I can have nested copy-on-write
images?
Right now I'm leaning towards doing my migrations the hard way instead,
by simply copying the raw instance files across and then mucking around
in the nova database. I'd love it if someone could steer me to a proper
API-based approach though!
Thanks!
-Andrew
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