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Re:What happens under the hood?

Posted by: Anonymous Coward on July 30, 2006 11:55 AM
Good explanation. I would add the following warning:

Xen is not yet ready for production purposes with anything you are concerned about losing. Even if you want to try it on something that isn't mission-critical, I recommend having a backup solution ready. Xen is really broken and still in its infancy.

By default all Direct IO is cached in linux. The actual writeback is deferred. Now, if there is direct io done by a Xen domU instance, the host tells the guest that the write succeeded. Yet, it is actually sitting in cache.

Therefore, Xen does not correctly track dirty blocks of memory. This is an issue even if you don't want to use live migration.

Wait for the Xen folks to patch the dirty block issue.

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