.`RocksDB` is enabled as an option to replace `levelDB`
This update enables an option to use the `RocksDB` back end for the `omap` database as opposed to `levelDB`. `RocksDB` uses the multi-threading mechanism in compaction so that it better handles the situation when the `omap` directories become very large (more than 40 G). `LevelDB` compaction takes a lot of time in such a situation and causes OSD daemons to time out.
For details about conversion from `levelDB` to `RocksDB`, see the link:https://access.redhat.com/solutions/3210951[Ceph - Steps to convert OSD omap backend from leveldb to rocksdb] solution on Red Hat Customer Portal.