A 'ceph pg scrub' resulted in a read error on one of the OSDs. What does it mean?

Solution In Progress - Updated -

Environment

  • Inktank Ceph Enterprise 1.1

Issue

  • A 'ceph pg scrub <pg.id>' resulted in a read error on one of the OSDs.

  • A subsequent 'ceph health detail' shows scrub errors.

# ceph health detail
HEALTH_ERR 1 pgs inconsistent; 1 scrub errors
pg 40.17ae is active+clean+inconsistent, acting [145,107,101]
1 scrub errors
  • A look into the OSD logs [145, 107, 101] shows a lossy connection
# cat ceph-osd.101.log | grep 40.17ae
2015-04-27 16:47:29.635290 7f60d84bc700  0 -- AA.BB.CC.DD:6800/4027434 submit_message osd_sub_op(unknown.0.0:0 40.17ae 0//0//-1 [scrub-map] v 0'0 snapset=0=[]:[] snapc=0=[]) v11 remote, EE.FF.GG.HH:6808/10555, failed lossy con, dropping message 0x17ac1800
2015-04-27 18:30:39.344752 7f60d8cbd700  0 -- AA.BB.CC.DD:6820/5027434 submit_message osd_sub_op(unknown.0.0:0 40.17ae 0//0//-1 [scrub-map] v 0'0 snapset=0=[]:[] snapc=0=[]) v11 remote, EE.FF.GG.HH:6808/10555, failed lossy con, dropping message 0x2ed83800

Resolution

  • From the OSD logs, it seems that the scrub error was caused due to a hardware problem.

  • Running a hardware check along with using 'smartd' is suggested. To know more on smartd, read https://access.redhat.com/solutions/1456.

  • In order to bring the Ceph cluster to an active state as quickly as possible, the OSD can be marked as out so that the PGs would get another OSD allocated.

  • To set the OSD as out, execute:

# ceph osd out {osd.number}
  • Once the cluster recovers and reach a clean state, the scrub can be started once again to confirm that the data is indeed correct.

Root Cause

  • Based on the output of the scrub and OSD logs, it seems that there was a hardware error involved here.

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