Hi Ceph Users, We plan to add 20 storage nodes to our existing cluster of 40 nodes, each node has 36 x 5.458 TiB drives. We plan to add the storage such that all new OSDs are prepared, activated and ready to take data but not until we start slowly increasing their weightings. We also expect this not to cause any backfilling before we adjust the weightings.
When testing the deployment on our development cluster, adding a new OSD to the host bucket with a crush weight of 5.458 and an OSD reweight of 0 (we have set "noin") causes the acting sets of a few pools to change, thus triggering backfilling. Interestingly, none of the pool backfilling have the new OSD in their acting set. This was not what we expected, so I have to ask, is what we are trying to achieve possible and how best we should go about doing it. Commands run: ceph osd crush add osd.43 0 host=ceph-sn833 - causes no backfilling ceph osd crush add osd.44 5.458 host=ceph-sn833 - does cause backfilling For multiple hosts and OSDs, we plan to prepare a new crushmap and inject that into the cluster. Best wishes, Bruno Bruno Canning LHC Data Store System Administrator Scientific Computing Department STFC Rutherford Appleton Laboratory Harwell Oxford Didcot OX11 0QX Tel. +44 ((0)1235) 446621
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