Ceph » CephFS

Source: https://github.com/ceph/ceph/pull/42295#discussion_r670827459

Currently, to recover a file system after recovering monitor store, you need to stop all the MDSs, create FSMap with defaults using `fs new` command, execute `fs reset` command to get file system' rank 0 into failed state, and then restart MDSs.

If the rank 0 of filesystem is not set to failed state, then the MDS that takes up rank 0 doesn't read the existing in RADOS metadata and starts overwriting it. So the fiile system is not recovered. By allowing the `fs new` command to optionally set rank 0 to failed state instead of creating state, we may able to avoid the need to stop all the MDSs and execute `fs reset` command.