Hello, everyone! We have recently upgraded our Ceph pool to the latest Luminous release. On one of the servers that we used as Ceph clients we had several freeze issues, which we empirically linked to the concurrent usage of some I/O operations - writing in an LXD container (backed by Ceph) while there was an ongoing PG rebalancing. We searched for the issue's cause through the logs, but we haven't found anything useful.
At that time the server was running Ubuntu 16 with a 4.5 kernel. We thought an upgrade to the latest HWE kernel (4.10) would help, but we had the same freezing issues after the kernel upgrade. Of course, we're aware that we have tried to fix / avoid the issue without understanding it's cause. After seeing the OS recommendations from the Ceph page <https://github.com/ceph/ceph/blob/master/doc/start/os-recommendations.rst>, we reinstalled the server (and got the 4.4 kernel), we ran into a feature set mismatch issue when mounting a RBD image. We concluded <http://cephnotes.ksperis.com/blog/2014/01/21/feature-set-mismatch-error-on-ceph-kernel-client> that the feature set requires a kernel > 4.5. Our question - how would you recommend us to proceed? Shall we re-upgrade to the HWE kernel (4.10) or to another kernel version? Would you recommend an alternative solution? Thank you very much, we're looking forward for your advice. Kind regards, Bogdan
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