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Re: [Xen-devel] Domain save/migrate issue

Steven Hand wrote:
  I tend to agree, it's about having orthogonal APIs, I think you can build
the current behaviour by a sequence of the simpler save and a destroy (though
it would not be atomic anymore). Is there any strong reason a saved domain
must not be left running ?

Unless you also have some way to simulataneously snapshot the file
system, it is not safe to allow the guest to continue and then later
resume the checkpointed version.
There are storage devices that provide this capability. Also, Dan Smith is working on a COW device for Xen that could be used to checkpoint a storage device.

However, there's a fair bit of work that would be needed to allow for light-weight checkpointing. A domain has to be suspended for the checkpoint to finish (although presumably one could use a similar as live migration to get most of the way there). Today, in Xen, there is no way to get out of a suspended state.

If a domain could leave the suspended state, it would make checkpointing pretty cheap. Also, presumably, it would simplify rebooting because instead of having to recreate a domain on reboot, the hypervisor could just reinit it. Of course, it would need some way of knowing how to build the domain...


Anthony Liguori

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