[ceph-users] Move on cephfs not O(1)?

Some time ago I made a surprising observation. I reorganised a directory structure and needed to move a folder one level up with a command like mv A/B/ B B contained something like 9TB in very large files. To my surprise, this command didn't return for a couple of minutes and I started to look what was going on. What I discovered was, that the mv command actually performed a full copy with a subsequent remove. I had to wait for several hours for the move to complete. I tried to reproduce this today to collect further information. However, this behaviour seems not reproducible. No matter what I try, mv completes almost instantly. I was running the original mv on mimic 13.2.2 and retried now with mimic 13.2.8. In addition, there was an OS upgrade from Centos 7.6 to 7.7. I'm using the kernel-ml versions (5.xxx). Only one cephfs mount was present at all times. My questions are: 1) Was there a change from 13.2.2 to 13.2.8 explaining this? 2) Are there (rare) conditions under which an mv on cephfs becomes a cp+rm? 3) Am I seeing ghosts? Thanks for clues and best regards, ================= Frank Schilder AIT Risø Campus Bygning 109, rum S14