Problem:
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1. rbd-nbd by default logs to /var/log/ceph/ceph-client.admin.log,
Unfortunately, container doesn't have /var/log/ceph directory hence
rbd-nbd is not logging now.
2. Rbd-nbd logs are not persistent across nodeplugin restarts.
Solution:
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Provide a host path so that log directory is made available, and the
logs persist on the hostnode across container restarts.
Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>