By default, Ceph will warn when OSD utilization approaches 85%, and it will stop write I/O to the OSD when it reaches 95%. If, for some reason, the OSD completely fills up to 100%, then the OSD is likely to crash and will refuse to come back online. An OSD that is above the 85% warning level will also refuse to participate in backfilling, so the recovery of the cluster may be impacted when OSDs are in a near full state.
Before covering the troubleshooting steps around full OSDs, it is highly recommended that you monitor the capacity utilization of your OSDs, as described in the monitoring chapter. This will give you advanced warning as OSDs approach the near_full warning threshold.
If you find yourself in a situation where your cluster is above the near full warning state, you have two main options:
- Add some more OSDs.
- Delete some data.
However, in the real world, both of these are either impossible...