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
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