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[Jānis Ģeņģeris <janis.gengeris@xxxxxxxxx>]

Hello all,

I would like to know the available solutions that are used regarding to
backing up and/or snapshotting running
instances on compute nodes. Documentation does not mention anything related
to this. With snapshots I don't mean
the current snapshot mechanism, that imports image of the running VM into
glance. I'm using KVM, but this is
significant for any hypervisor.

Why is this important?
Consider simple scenario when hardware on compute node fails and the node
goes down immediately and is not recoverable
in reasonable time. The images of the running instances are also lost.
Shared file system is not considered here as it
may cause IO bottlenecks and adds another layer of complexity.

There have been a few discussions on the the list about this problem, but
none have really answered the question.

The documentation speaks of disaster recovery when power loss have happened
and failed compute node recovery from
shared file system. But don't cover the case without shared file system.

I can think of few solutions currently (for KVM):
a) using LVM images for VMs, and making LVM logical volume snapshots, but
then the current nova snapshot mechanism
will not work (from the docs - 'current snapshot mechanism in OpenStack
Compute works only with instances backed
with Qcow2 images');
b) snapshot machines with OpenStack snapshotting mechanism, but this
doesn't fit somehow, because it has
other goal than creating backups, will be slow and pollute the glance image
space;

Regards
--janis