ceph version 12.2.13 luminous (stable) My whole ceph cluster went to kind of read only state. Ceph status showed that client reads is 0 op/s for whole cluster. There was normal amount of writes going on. I checked health and it said: # ceph health detail HEALTH_WARN Reduced data availability: 1 pg inactive, 1 pg peering PG_AVAILABILITY Reduced data availability: 1 pg inactive, 1 pg peering pg 26.13b is stuck peering for 25523.506788, current state peering, last acting [2,0,33] All osds showed to be up and all monitors are good. All pools are 3/2 (size/min) and space usage ~30%. I fixed this by restarting forst osd.2 (nothing happened) and then restarted osd.0. After that everyting went back to normal. So what can cause "stuck peering" and how can i prevent this event from happening again?