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[Xen-devel] Migration filesystem coherency?


I thought I had a workaround for live migration crashing (I've been looking at the SLES 3.0.2 9742c code.), but I found that I was getting filesystem errors. I'm wondering if the problem is races in data being written to the backing storage.

When migrating a domain, before the domain is started on the new host, you have to guarantee that all the domU vbd data is out of the block cache and written to the backing device. (In the case of a loopback device, whether this is sufficient depends on the cross-host coherency guarantees of the backing filesystem.) I cannot see that this takes place synchronously with the migration process. To me it looks like that the teardown/flush of the backing device depends on the action of the xenbus and the hotplug scripts and looks asynchronous to the migration process.

So, am I right that there is a really a problem here or is there some other way the vbd data is getting flushed during migrate?


John Byrne

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