Hi, ceph version 14.2.1 (d555a9489eb35f84f2e1ef49b77e19da9d113972) nautilus (stable) Yesterday noticed unexpected behavior, probably bug. It seems ceph wrongly calculates osd size if it is replaced with smaller disk. In detail: Starting point: 1 osd disk had failed, ceph had reballanced and osd was marked down. I did remove failed disk(10TB) and replaced with smaller 6TB. Followed disk replacement instructions here: https://docs.ceph.com/docs/mimic/rados/operations/add-or-rm-osds/ Destroy the OSD first: ceph osd destroy {id} --yes-i-really-mean-it Zap a disk for the new OSD, if the disk was used before for other purposes. It’s not necessary for a new disk: ceph-volume lvm zap /dev/sdX Prepare the disk for replacement by using the previously destroyed OSD id: ceph-volume lvm prepare --osd-id {id} --data /dev/sdX And activate the OSD: ceph-volume lvm activate {id} {fsid} I skipped this as was not clear what fsid was needed(probably ceph cluster fsid} and just started osd systemctl start ceph-osd@29 OSD came up and reballance started. After some time ceph started to complain following: # ceph health detail HEALTH_WARN 1 nearfull osd(s); 19 pool(s) nearfull; 10 pgs not deep-scrubbed in time OSD_NEARFULL 1 nearfull osd(s) osd.29 is near full #ceph osd df tree -------------------- ID CLASS WEIGHT REWEIGHT SIZE RAW USE DATA OMAP META AVAIL %USE VAR PGS STATUS TYPE NAME ... 29 hdd 9.09569 1.00000 5.5 TiB 3.3 TiB 3.3 TiB 981 KiB 4.9 GiB 2.2 TiB 59.75 0.99 590 up osd.29 Later I noticed that weight of osd.29 was still 9.09569 as for replaced 10TB disk. I did: ceph osd crush reweight osd.29 5.45789 Things got back to normal after reballance. Got impression that ceph did not realize that osd had been replaced with smaller disk. Could that be because I skipped activation step? Or this is a bug. Best regards, Ugis
