Yes, this is a consequence of co-locating the MDS and monitors — if the MDS
reports to its co-located monitor and both fail, the monitor cluster has to
go through its own failure detection and then wait for a full MDS timeout
period after that before it marks the MDS down. :(
We might conceivably be able to optimize for this, but there's not a
general solution. If you need to co-locate, one thing that would make it
better without being a lot of work is trying to have the MDS connect to one
of the monitors on a different host. You can do that by just restricting
the list of monitors you feed it in the ceph.conf, although it's not a
guarantee that will *prevent* it from connecting to its own monitor if
there are failures or reconnects after first startup.
-Greg
On Thu, Aug 30, 2018 at 8:38 AM William Lawton <william.law...@irdeto.com>
wrote:
> Hi.
>
>
>
> We have a 5 node Ceph cluster (refer to ceph -s output at bottom of
> email). During resiliency tests we have an occasional problem when we
> reboot the active MDS instance and a MON instance together i.e.
> dub-sitv-ceph-02 and dub-sitv-ceph-04. We expect the MDS to failover to
> the standby instance dub-sitv-ceph-01 which is in standby-replay mode, and
> 80% of the time it does with no problems. However, 20% of the time it
> doesn’t and the MDS_ALL_DOWN health check is not cleared until 30 seconds
> later when the rebooted dub-sitv-ceph-02 and dub-sitv-ceph-04 instances
> come back up.
>
>
>
> When the MDS successfully fails over to the standby we see in the ceph.log
> the following:
>
>
>
> 2018-08-25 00:30:02.231811 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 50 : cluster [ERR] Health check failed: 1 filesystem is offline
> (MDS_ALL_DOWN)
>
> 2018-08-25 00:30:02.237389 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 52 : cluster [INF] Standby daemon mds.dub-sitv-ceph-01 assigned to
> filesystem cephfs as rank 0
>
> 2018-08-25 00:30:02.237528 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 54 : cluster [INF] Health check cleared: MDS_ALL_DOWN (was: 1 filesystem is
> offline)
>
>
>
> When the active MDS role does not failover to the standby the MDS_ALL_DOWN
> check is not cleared until after the rebooted instances have come back up
> e.g.:
>
>
>
> 2018-08-25 03:30:02.936554 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 55 : cluster [ERR] Health check failed: 1 filesystem is offline
> (MDS_ALL_DOWN)
>
> 2018-08-25 03:30:04.235703 mon.dub-sitv-ceph-05 mon.2 10.18.186.208:6789/0
> 226 : cluster [INF] mon.dub-sitv-ceph-05 calling monitor election
>
> 2018-08-25 03:30:04.238672 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 56 : cluster [INF] mon.dub-sitv-ceph-03 calling monitor election
>
> 2018-08-25 03:30:09.242595 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 57 : cluster [INF] mon.dub-sitv-ceph-03 is new leader, mons
> dub-sitv-ceph-03,dub-sitv-ceph-05 in quorum (ranks 0,2)
>
> 2018-08-25 03:30:09.252804 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 62 : cluster [WRN] Health check failed: 1/3 mons down, quorum
> dub-sitv-ceph-03,dub-sitv-ceph-05 (MON_DOWN)
>
> 2018-08-25 03:30:09.258693 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 63 : cluster [WRN] overall HEALTH_WARN 2 osds down; 2 hosts (2 osds) down;
> 1/3 mons down, quorum dub-sitv-ceph-03,dub-sitv-ceph-05
>
> 2018-08-25 03:30:10.254162 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 64 : cluster [WRN] Health check failed: Reduced data availability: 2 pgs
> inactive, 115 pgs peering (PG_AVAILABILITY)
>
> 2018-08-25 03:30:12.429145 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 66 : cluster [WRN] Health check failed: Degraded data redundancy: 712/2504
> objects degraded (28.435%), 86 pgs degraded (PG_DEGRADED)
>
> 2018-08-25 03:30:16.137408 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 67 : cluster [WRN] Health check update: Reduced data availability: 1 pg
> inactive, 69 pgs peering (PG_AVAILABILITY)
>
> 2018-08-25 03:30:17.193322 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 68 : cluster [INF] Health check cleared: PG_AVAILABILITY (was: Reduced data
> availability: 1 pg inactive, 69 pgs peering)
>
> 2018-08-25 03:30:18.432043 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 69 : cluster [WRN] Health check update: Degraded data redundancy: 1286/2572
> objects degraded (50.000%), 166 pgs degraded (PG_DEGRADED)
>
> 2018-08-25 03:30:26.139491 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 71 : cluster [WRN] Health check update: Degraded data redundancy: 1292/2584
> objects degraded (50.000%), 166 pgs degraded (PG_DEGRADED)
>
> 2018-08-25 03:30:31.355321 mon.dub-sitv-ceph-04 mon.1 10.18.53.155:6789/0
> 1 : cluster [INF] mon.dub-sitv-ceph-04 calling monitor election
>
> 2018-08-25 03:30:31.371519 mon.dub-sitv-ceph-04 mon.1 10.18.53.155:6789/0
> 2 : cluster [WRN] message from mon.0 was stamped 0.817433s in the future,
> clocks not synchronized
>
> 2018-08-25 03:30:32.175677 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 72 : cluster [INF] mon.dub-sitv-ceph-03 calling monitor election
>
> 2018-08-25 03:30:32.175864 mon.dub-sitv-ceph-05 mon.2 10.18.186.208:6789/0
> 227 : cluster [INF] mon.dub-sitv-ceph-05 calling monitor election
>
> 2018-08-25 03:30:32.180615 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 73 : cluster [INF] mon.dub-sitv-ceph-03 is new leader, mons
> dub-sitv-ceph-03,dub-sitv-ceph-04,dub-sitv-ceph-05 in quorum (ranks 0,1,2)
>
> 2018-08-25 03:30:32.189593 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 78 : cluster [INF] Health check cleared: MON_DOWN (was: 1/3 mons down,
> quorum dub-sitv-ceph-03,dub-sitv-ceph-05)
>
> 2018-08-25 03:30:32.190820 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 79 : cluster [WRN] mon.1 10.18.53.155:6789/0 clock skew 0.811318s > max
> 0.05s
>
> 2018-08-25 03:30:32.194280 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 80 : cluster [WRN] overall HEALTH_WARN 2 osds down; 2 hosts (2 osds) down;
> Degraded data redundancy: 1292/2584 objects degraded (50.000%), 166 pgs
> degraded
>
> 2018-08-25 03:30:35.076121 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 83 : cluster [INF] daemon mds.dub-sitv-ceph-02 restarted
>
> 2018-08-25 03:30:35.270222 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 85 : cluster [WRN] Health check failed: 1 filesystem is degraded
> (FS_DEGRADED)
>
> 2018-08-25 03:30:35.270267 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 86 : cluster [ERR] Health check failed: 1 filesystem is offline
> (MDS_ALL_DOWN)
>
> 2018-08-25 03:30:35.282139 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 88 : cluster [INF] Standby daemon mds.dub-sitv-ceph-01 assigned to
> filesystem cephfs as rank 0
>
> 2018-08-25 03:30:35.282268 mon.dub-sitv-ceph-03 mon.0 10.18.53.32:6789/0
> 89 : cluster [INF] Health check cleared: MDS_ALL_DOWN (was: 1 filesystem is
> offline)
>
>
>
> In the MDS log we’ve noticed that when the issue occurs, at precisely the
> time when the active MDS/MON nodes are rebooted, the standby MDS instance
> briefly stops logging replay_done (as standby). This is shown in the log
> exert below where there is a 9s gap in these logs.
>
>
>
> 2018-08-25 03:30:00.085 7f3ab9b00700 1 mds.0.0 replay_done (as standby)
>
> 2018-08-25 03:30:01.091 7f3ab9b00700 1 mds.0.0 replay_done (as standby)
>
> 2018-08-25 03:30:10.332 7f3ab9b00700 1 mds.0.0 replay_done (as standby)
>
> 2018-08-25 03:30:11.333 7f3abb303700 1 mds.0.0 replay_done (as standby)
>
>
>
> I’ve tried to reproduce the issue by rebooting each MDS instance in turn
> repeatedly 5 minutes apart but so far haven’t been able to do so, so my
> assumption is that rebooting the MDS and a MON instance at the same time is
> a significant factor.
>
>
>
> Our mds_standby* configuration is set as follows:
>
>
>
> "mon_force_standby_active": "true",
>
> "mds_standby_for_fscid": "-1",
>
> "mds_standby_for_name": "",
>
> "mds_standby_for_rank": "0",
>
> "mds_standby_replay": "true",
>
>
>
> The cluster status is as follows:
>
>
>
> cluster:
>
> id: f774b9b2-d514-40d9-85ab-d0389724b6c0
>
> health: HEALTH_OK
>
>
>
> services:
>
> mon: 3 daemons, quorum
> dub-sitv-ceph-03,dub-sitv-ceph-04,dub-sitv-ceph-05
>
> mgr: dub-sitv-ceph-04(active), standbys: dub-sitv-ceph-03,
> dub-sitv-ceph-05
>
> mds: cephfs-1/1/1 up {0=dub-sitv-ceph-02=up:active}, 1
> up:standby-replay
>
> osd: 4 osds: 4 up, 4 in
>
>
>
> data:
>
> pools: 2 pools, 200 pgs
>
> objects: 554 objects, 980 MiB
>
> usage: 7.9 GiB used, 1.9 TiB / 2.0 TiB avail
>
> pgs: 200 active+clean
>
>
>
> io:
>
> client: 1.5 MiB/s rd, 810 KiB/s wr, 286 op/s rd, 218 op/s wr
>
>
>
> Hope someone can help!
>
> *William Lawton*
>
>
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>
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