Document caching issue with local nbd servers #123
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When connecting to local NBD servers, caching has to be disabled on the nbd daemon side in order to avoid deadlocks. We'll document this and provide a qemu-storage-daemon example. Note that this issue does not affect Ceph. Another way to mitigate it would be to forward LUN resets to the NBD daemon and reestablish the NBD connection. This would still be less than ideal since IO would be stuck for 30s, until Storport issues a reset. It would also require some changes on the driver side (e.g. separate queue for control commands, otherwise the dispatchers might be stuck with IO operations). Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>
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When connecting to local NBD servers, caching has to be disabled on the nbd daemon side in order to avoid deadlocks. We'll document this and provide a qemu-storage-daemon example.
Note that this issue does not affect Ceph.
Another way to mitigate it would be to forward LUN resets to the NBD daemon and reestablish the NBD connection. This would still be less than ideal since IO would be stuck for 30s, until Storport issues a reset. It would also require some changes on the driver side (e.g. separate queue for control commands, otherwise the dispatchers might be stuck with IO operations).