Hi Andreas,
I made exactly the same observation in another scenario. I added some OSDs while other OSDs were down.
This is expected.
The crush map is an a-priory algorithm to compute the location of objects without contacting a central server. Hence, *any*change of a crush map while an OSD is down will lead to a change of locations of objects/PGs of the down OSD. Consequently, these objects/PGs will become degraded, because no up OSD reports these. Once the peering is over after setting the weight to 0, the cluster must assume they are lost.
Changing a weight is a change of the crush map.
The way to get the cluster to re-scan after starting the down OSDs is to restore the crush map to exactly the state as it was before the OSD went down. In your case,
- starting the down OSD,
- setting weight back to original value
will find all missing objects. After the cluster is clean, set the weight back to 0 and now the OSD will be vacated as expected.
Best regards,
=================
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14
________________________________________
From: Andras Pataki <apataki@xxxxxxxxxxxxxxxxxxxxx>
Sent: 18 May 2020 22:25:37
To: ceph-users
Subject: Reweighting OSD while down results in undersized+degraded PGs
In a recent cluster reorganization, we ended up with a lot of
undersized/degraded PGs and a day of recovery from them, when all we
expected was moving some data around. After retracing my steps, I found
something odd. If I crush reweight an OSD to 0 while it is down - it
results in the PGs of that OSD ending up degraded even after the OSD is
restarted. If I do the same reweighting while the OSD is up - data gets
moved without any degraded/undersized states. I would not expect this -
so I wonder if this is a bug or is somehow intended. This is on ceph
Nautilus 14.2.8. Below are the details.
Andras
First the case that works as I would expect:
# Healthy cluster ...
[root@xorphosd00 ~]# ceph -s
cluster:
id: 86d8a1b9-761b-4099-a960-6a303b951236
health: HEALTH_WARN
noout,nobackfill,noscrub,nodeep-scrub flag(s) set
services:
mon: 3 daemons, quorum xorphmon00,xorphmon01,xorphmon02 (age 11d)
mgr: xorphmon01(active, since 6w), standbys: xorphmon02, xorphmon00
mds: cephfs:1 {0=xorphmon02=up:active} 1 up:standby
osd: 270 osds: 270 up (since 2m), 270 in (since 4h)
flags noout,nobackfill,noscrub,nodeep-scrub
data:
pools: 4 pools, 5312 pgs
objects: 75.87M objects, 287 TiB
usage: 864 TiB used, 1.1 PiB / 1.9 PiB avail
pgs: 5312 active+clean
# Reweight an OSD to 0
[root@xorphosd00 ~]# ceph osd crush reweight osd.0 0.0
reweighted item id 0 name 'osd.0' to 0 in crush map
# Crush map changes - data movement is set up, no degraded PGs:
[root@xorphosd00 ~]# ceph -s
cluster:
id: 86d8a1b9-761b-4099-a960-6a303b951236
health: HEALTH_WARN
noout,nobackfill,noscrub,nodeep-scrub flag(s) set
services:
mon: 3 daemons, quorum xorphmon00,xorphmon01,xorphmon02 (age 11d)
mgr: xorphmon01(active, since 6w), standbys: xorphmon02, xorphmon00
mds: cephfs:1 {0=xorphmon02=up:active} 1 up:standby
osd: 270 osds: 270 up (since 10m), 270 in (since 5h); 175 remapped pgs
flags noout,nobackfill,noscrub,nodeep-scrub
data:
pools: 4 pools, 5312 pgs
objects: 75.87M objects, 287 TiB
usage: 864 TiB used, 1.1 PiB / 1.9 PiB avail
pgs: 2562045/232996662 objects misplaced (1.100%)
5137 active+clean
172 active+remapped+backfilling
3 active+remapped+backfill_wait
# Reweight it back to the original weight
[root@xorphosd00 ~]# ceph osd crush reweight osd.0 8.0
# Cluster goes back to clean
reweighted item id 0 name 'osd.0' to 8 in crush map
[root@xorphosd00 ~]# ceph -s
cluster:
id: 86d8a1b9-761b-4099-a960-6a303b951236
health: HEALTH_WARN
noout,nobackfill,noscrub,nodeep-scrub flag(s) set
services:
mon: 3 daemons, quorum xorphmon00,xorphmon01,xorphmon02 (age 11d)
mgr: xorphmon01(active, since 6w), standbys: xorphmon02, xorphmon00
mds: cephfs:1 {0=xorphmon02=up:active} 1 up:standby
osd: 270 osds: 270 up (since 11m), 270 in (since 5h)
flags noout,nobackfill,noscrub,nodeep-scrub
data:
pools: 4 pools, 5312 pgs
objects: 75.87M objects, 287 TiB
usage: 864 TiB used, 1.1 PiB / 1.9 PiB avail
pgs: 5312 active+clean
#
# Now the problematic case
#
# Stop an OSD
[root@xorphosd00 ~]# systemctl stop ceph-osd@0
# We get degraded PGs - as expected
[root@xorphosd00 ~]# ceph -s
cluster:
id: 86d8a1b9-761b-4099-a960-6a303b951236
health: HEALTH_WARN
noout,nobackfill,noscrub,nodeep-scrub flag(s) set
1 osds down
Degraded data redundancy: 873964/232996662 objects degraded
(0.375%), 82 pgs degraded
services:
mon: 3 daemons, quorum xorphmon00,xorphmon01,xorphmon02 (age 11d)
mgr: xorphmon01(active, since 6w), standbys: xorphmon02, xorphmon00
mds: cephfs:1 {0=xorphmon02=up:active} 1 up:standby
osd: 270 osds: 269 up (since 16s), 270 in (since 5h)
flags noout,nobackfill,noscrub,nodeep-scrub
data:
pools: 4 pools, 5312 pgs
objects: 75.87M objects, 287 TiB
usage: 864 TiB used, 1.1 PiB / 1.9 PiB avail
pgs: 873964/232996662 objects degraded (0.375%)
5230 active+clean
82 active+undersized+degraded
# Reweight the OSD to 0:
[root@xorphosd00 ~]# ceph osd crush reweight osd.0 0.0
# Still degraded - as expected
reweighted item id 0 name 'osd.0' to 0 in crush map
[root@xorphosd00 ~]# ceph -s
cluster:
id: 86d8a1b9-761b-4099-a960-6a303b951236
health: HEALTH_WARN
noout,nobackfill,noscrub,nodeep-scrub flag(s) set
1 osds down
Degraded data redundancy: 873964/232996662 objects degraded
(0.375%), 82 pgs degraded
services:
mon: 3 daemons, quorum xorphmon00,xorphmon01,xorphmon02 (age 11d)
mgr: xorphmon01(active, since 6w), standbys: xorphmon02, xorphmon00
mds: cephfs:1 {0=xorphmon02=up:active} 1 up:standby
osd: 270 osds: 269 up (since 59s), 270 in (since 5h); 175 remapped pgs
flags noout,nobackfill,noscrub,nodeep-scrub
data:
pools: 4 pools, 5312 pgs
objects: 75.87M objects, 287 TiB
usage: 864 TiB used, 1.1 PiB / 1.9 PiB avail
pgs: 873964/232996662 objects degraded (0.375%)
1688081/232996662 objects misplaced (0.725%)
5137 active+clean
93 active+remapped+backfilling
82 active+undersized+degraded+remapped+backfilling
# Restarting the OSD
[root@xorphosd00 ~]# systemctl start ceph-osd@0
# And the PGs still stay degraded - THIS IS UNEXPECTED!!!
[root@xorphosd00 ~]# ceph -s
cluster:
id: 86d8a1b9-761b-4099-a960-6a303b951236
health: HEALTH_WARN
noout,nobackfill,noscrub,nodeep-scrub flag(s) set
Degraded data redundancy: 873964/232996662 objects degraded
(0.375%), 82 pgs degraded
services:
mon: 3 daemons, quorum xorphmon00,xorphmon01,xorphmon02 (age 11d)
mgr: xorphmon01(active, since 6w), standbys: xorphmon02, xorphmon00
mds: cephfs:1 {0=xorphmon02=up:active} 1 up:standby
osd: 270 osds: 270 up (since 14s), 270 in (since 5h); 175 remapped pgs
flags noout,nobackfill,noscrub,nodeep-scrub
data:
pools: 4 pools, 5312 pgs
objects: 75.87M objects, 287 TiB
usage: 864 TiB used, 1.1 PiB / 1.9 PiB avail
pgs: 873964/232996662 objects degraded (0.375%)
1688081/232996662 objects misplaced (0.725%)
5137 active+clean
93 active+remapped+backfilling
82 active+undersized+degraded+remapped+backfilling
# Now for something even more odd - reweight the OSD back to its
original weigh
# and all the data gets magically FOUND again on that OSD!!!
[root@xorphosd00 ~]# ceph osd crush reweight osd.0 8.0
reweighted item id 0 name 'osd.0' to 8 in crush map
[root@xorphosd00 ~]# ceph -s
cluster:
id: 86d8a1b9-761b-4099-a960-6a303b951236
health: HEALTH_WARN
noout,nobackfill,noscrub,nodeep-scrub flag(s) set
services:
mon: 3 daemons, quorum xorphmon00,xorphmon01,xorphmon02 (age 11d)
mgr: xorphmon01(active, since 6w), standbys: xorphmon02, xorphmon00
mds: cephfs:1 {0=xorphmon02=up:active} 1 up:standby
osd: 270 osds: 270 up (since 51s), 270 in (since 5h)
flags noout,nobackfill,noscrub,nodeep-scrub
data:
pools: 4 pools, 5312 pgs
objects: 75.87M objects, 287 TiB
usage: 864 TiB used, 1.1 PiB / 1.9 PiB avail
pgs: 5312 active+clean
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