Hi Sam,
> The pg might also be degraded right after a map change which changes the
> up/acting sets since the few objects updated right before the map change
> might be new on some replicas and old on the other replicas. While in that
> state, those specific objects are degraded, and the pg would report
> degraded until they are recovered (which would happen asap, prior to
> backfilling the new replica). -Sam
That sounds like only a few PGs should be degraded. I instead have about 45%
(and higher earlier).
# ceph -s
cluster 7797e50e-f4b3-42f6-8454-2e2b19fa41d6
health HEALTH_WARN
2081 pgs backfill
6745 pgs degraded
17 pgs recovering
6728 pgs recovery_wait
6745 pgs stuck degraded
8826 pgs stuck unclean
recovery 2530124/5557452 objects degraded (45.527%)
recovery 33594/5557452 objects misplaced (0.604%)
monmap e5: 3 mons at
{mon01=128.104.164.197:6789/0,mon02=128.104.164.198:6789/0,mon03=10.128.198.51:6789/0}
election epoch 16458, quorum 0,1,2 mon03,mon01,mon02
mdsmap e3032: 1/1/1 up {0=mds01.hep.wisc.edu=up:active}
osdmap e149761: 27 osds: 27 up, 27 in; 2083 remapped pgs
pgmap v13464928: 18432 pgs, 9 pools, 5401 GB data, 1364 kobjects
11122 GB used, 11786 GB / 22908 GB avail
2530124/5557452 objects degraded (45.527%)
33594/5557452 objects misplaced (0.604%)
9606 active+clean
6726 active+recovery_wait+degraded
2081 active+remapped+wait_backfill
17 active+recovering+degraded
2 active+recovery_wait+degraded+remapped
recovery io 24861 kB/s, 6 objects/s
Chad.
>
> ----- Original Message -----
> From: "Chad William Seys" <cwseys@xxxxxxxxxxxxxxxx>
> To: "ceph-users" <ceph-users@xxxxxxxx>
> Sent: Monday, July 27, 2015 12:27:26 PM
> Subject: why are there "degraded" PGs when adding OSDs?
>
> Hi All,
>
> I recently added some OSDs to the Ceph cluster (0.94.2). I noticed that
> 'ceph -s' reported both misplaced AND degraded PGs.
>
> Why should any PGs become degraded? Seems as though Ceph should only be
> reporting misplaced PGs?
>
> From the Giant release notes:
> Degraded vs misplaced: the Ceph health reports from ‘ceph -s’ and related
> commands now make a distinction between data that is degraded (there are
> fewer than the desired number of copies) and data that is misplaced (stored
> in the wrong location in the cluster). The distinction is important because
> the latter does not compromise data safety.
>
> Does Ceph delete some replicas of the PGs (leading to degradation) before
> re- replicating on the new OSD?
>
> This does not seem to be the safest algorithm.
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