Thanks Eugen, after enabling debugging temporarily, I have seen an error in the logs when creating the snapshot with mkdir snapshot in .snap including a suspicious line mds.0.server is a descendent of a subvolume dir Indeed, when doing a snapshot on the root folder of the filesystem (which works), the log files tell me the inode of the root directory and ceph daemon mds.MDSID dump inode 0x1 (for the root folder) outputs many information in json, including „is_subvolume“: true Indeed, for a different filesystem, where snapshots work as expected in root folder and subfolders, the same corresponding information from the root inode says „is_subvolume“: false. How can the root folder in a filesystem be a subvolume and what can I do to fix this? Also I am puzzled what has caused this problem… Thanks, Sophonet