Dear Cephers, I realized the following behaviour only recently:
1. Marking an OSD "out" sets the weight to zero and allows to migrate data away
(as long as it is up),
i.e. it is still considered as a "source" and nothing goes to degraded state
(so far, everything expected).
2. Restarting an "out" OSD, however, means it will come back with "0 pgs", and
if data was not fully migrated away yet,
it means the PGs which were still kept on it before will enter degraded
state since they now lack a copy / shard.
Is (2) expected?
If so, my understanding that taking an OSD "out" to let the data be migrated
away without losing any redundancy is wrong,
since redundancy will be lost as soon as the "out" OSD is restarted (e.g. due
to a crash, node reboot,...) and the only safe options would be:
1. Disable the automatic balancer.
2. Either adjust the weights of the OSDs to drain to zero, or use pg upmap to
drain them.
3. Reenable the automatic balancer only after having fully drained those OSDs
and performing the necessary intervention
(in our case, recreating the OSDs with a faster blockdb).
Is this correct?
Cheers,
Oliver
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