We now recommend against using ext4 as the underlying file system for Ceph OSDs, especially when RGW or other users of long RADOS object names are used. For more information about why, please see Filesystem Recommendations.

If you have an existing cluster that uses ext4 for the OSDs but uses only RBD and/or CephFS, then the ext4 limitations will not affect you. Before upgrading, be sure add the following to ceph.conf to allow the OSDs to start:

osd max object name len = 256 osd max object namespace len = 64

Keep in mind that if you set these lower object name limits and later decide to use RGW on this cluster, it will have problems storing S3/Swift objects with long names. This startup check can also be disabled via the below option, although this is not recommended: