Hi ceph users/devs, We've been encountering a strange issue with snapshots as part of a project to copy our large ceph file system to a backup in parallel across nodes.  We are taking a snapshot, and then doing a copy of the snapshot, which we expect to be static (unchanging) - using several clients in parallel - all kernel mounts.  Some clients are unable to open files and directories that are known to exist (were discovered traversing the file system on perhaps another node). After some playing around, I could reproduce the issue on a single node with just 'ls' as follows: # This file doesn't seems to exist - and some number of parent directories are also "missing": [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis/mutation_total_scores/C_32_S_to_W/gamess_io/gamess_qm_energy_thread0_2026_05_15_13_18_13.log ls: cannot access '/mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis/mutation_total_scores/C_32_S_to_W/gamess_io/gamess_qm_energy_thread0_2026_05_15_13_18_13.log': No such file or directory [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis/mutation_total_scores/C_32_S_to_W/gamess_io ls: cannot access '/mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis/mutation_total_scores/C_32_S_to_W/gamess_io': No such file or directory [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis/mutation_total_scores/C_32_S_to_W ls: cannot access '/mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis/mutation_total_scores/C_32_S_to_W': No such file or directory [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis/mutation_total_scores ls: cannot access '/mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis/mutation_total_scores': No such file or directory [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis ls: cannot access '/mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis': No such file or directory [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output ls: cannot access '/mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output': No such file or directory [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen ls: cannot access '/mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen': No such file or directory [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM ls: cannot access '/mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM': No such file or directory [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK ls: cannot access '/mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK': No such file or directory # Until we get to this 'Projects' parent directory, which seems to be there [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects drwxr-sr-x 45 1961 1961 46 Jun 8 14:02 /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects # GSK under it is still not there ... [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK ls: cannot access '/mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK': No such file or directory # But ... let's see if the "tickle" the Projects directory a bit ... [root@cephmds603 ~]# ls -l /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects > /dev/null # Now all subdirectories and the file in question immediately becomes visible: [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK drwxrwsr-x 5 1961 1961 3 May 7 17:18 /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM drwxrwsr-x 12 1961 1961 10 May 11 16:08 /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen drwxrwsr-x 5 1961 1961 3 May 11 16:18 /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen [root@cephmds603 ~]# ls -ld /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis/mutation_total_scores/C_32_S_to_W/gamess_io/gamess_qm_energy_thread0_2026_05_15_13_18_13.log -rw-rw-r-- 1 1961 1961 51538071 May 15 14:10 /mnt/ceph/users/.snap/sync-20260701-0904/bturzo/Projects/GSK/RosettaQM/af3_ensemble_gen/output/ddg_analysis/mutation_total_scores/C_32_S_to_W/gamess_io/gamess_qm_energy_thread0_2026_05_15_13_18_13.log # This is the kernel client 6.18.32 (relatively recent LTS kernel) with ceph squid 19.2.3: [root@cephmds603 ~]# uname -a Linux cephmds603 6.18.32.1.fi #4 SMP Mon May 18 11:45:58 EDT 2026 x86_64 x86_64 x86_64 GNU/Linux [root@cephmds603 ~]# ceph --version ceph version 19.2.3 (c92aebb279828e9c3c1f5d24613efca272649e62) squid (stable) [root@cephmds603 ~]# What is most interesting is that in the live tree (non-snapshotted tree) - the Projects directory exists, but everything under it has been removed! [root@cephmds600 ~]# ls -ld /mnt/ceph/users/bturzo/Projects/ drwxr-sr-x 43 1961 1961 45 Jul 17 11:56 /mnt/ceph/users/bturzo/Projects/ [root@cephmds600 ~]# ls -ld /mnt/ceph/users/bturzo/Projects/GSK ls: cannot access '/mnt/ceph/users/bturzo/Projects/GSK': No such file or directory Am I running into some known issue? This looks to be specific to some clients - i.e. some clients see the directory and some don't at the same point in time, i.e. this is perhaps a kclient problem? Any ideas/suggestions would be appreciated, Andras