We had the same problem yesterday. Out of our 5 node cluster 3 nodes suddenly rebooted while trying to migrate a VM from one node to another. Our cluster uses one network for Ceph and one network for cross VM connection and public network. We have been running stable like this for many years with lots of migrations no problems at all. Our current Proxmox version is Virtual Environment 4.4-22/2728f613. Now we had this occur twice within one day and i have really no idea what to look for in the syslog. Here is the syslog from when the second reboot happened. Wondering if the first entry contains the right clue, but i have no idea what it means.
Aug 28 11:33:51 Bucky corosync[1816]: [TOTEM ] A processor failed, forming new configuration.
Aug 28 11:34:01 Bucky corosync[1816]: [TOTEM ] A new membership (192.168.X.XXX:2708) was formed. Members left: 5
Aug 28 11:34:01 Bucky corosync[1816]: [TOTEM ] Failed to receive the leave message. failed: 5
Aug 28 11:34:01 Bucky corosync[1816]: [TOTEM ] Retransmit List: 1
Aug 28 11:34:01 Bucky pmxcfs[1702]: [dcdb] notice: members: 1/22496, 2/28978, 3/1717, 4/1702
Aug 28 11:34:01 Bucky pmxcfs[1702]: [dcdb] notice: starting data syncronisation
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: members: 1/22496, 2/28978, 3/1717, 4/1702
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: starting data syncronisation
Aug 28 11:34:01 Bucky corosync[1816]: [QUORUM] Members[4]: 3 4 1 2
Aug 28 11:34:01 Bucky corosync[1816]: [MAIN ] Completed service synchronization, ready to provide service.
Aug 28 11:34:01 Bucky pmxcfs[1702]: [dcdb] notice: received sync request (epoch 1/22496/0000000C)
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: received sync request (epoch 1/22496/00000008)
Aug 28 11:34:01 Bucky pmxcfs[1702]: [dcdb] notice: received all states
Aug 28 11:34:01 Bucky pmxcfs[1702]: [dcdb] notice: leader is 1/22496
Aug 28 11:34:01 Bucky pmxcfs[1702]: [dcdb] notice: synced members: 1/22496, 2/28978, 3/1717, 4/1702
Aug 28 11:34:01 Bucky pmxcfs[1702]: [dcdb] notice: all data is up to date
Aug 28 11:34:01 Bucky pmxcfs[1702]: [dcdb] notice: dfsm_deliver_queue: queue length 11
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: received all states
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: all data is up to date
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: dfsm_deliver_queue: queue length 111
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: received log
Aug 28 11:34:01 Bucky pmxcfs[1702]: [main] notice: ignore duplicate
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: received log
Aug 28 11:34:01 Bucky pmxcfs[1702]: [main] notice: ignore duplicate
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: received log
Aug 28 11:34:01 Bucky pmxcfs[1702]: [main] notice: ignore duplicate
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: received log
Aug 28 11:34:01 Bucky pmxcfs[1702]: [main] notice: ignore duplicate
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: received log
Aug 28 11:34:01 Bucky pmxcfs[1702]: [main] notice: ignore duplicate
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: received log
Aug 28 11:34:01 Bucky pmxcfs[1702]: [main] notice: ignore duplicate
Aug 28 11:34:01 Bucky pmxcfs[1702]: [status] notice: received log
Aug 28 11:34:01 Bucky pmxcfs[1702]: [main] notice: ignore duplicate
Aug 28 11:34:07 Bucky corosync[1816]: [TOTEM ] A new membership (192.168.X.XXX:2712) was formed. Members joined: 5
Aug 28 11:34:07 Bucky corosync[1816]: [TOTEM ] Retransmit List: 1
Aug 28 11:34:07 Bucky pmxcfs[1702]: [dcdb] notice: members: 1/22496, 2/28978, 3/1717, 4/1702, 5/1688
Aug 28 11:34:07 Bucky pmxcfs[1702]: [dcdb] notice: starting data syncronisation
Aug 28 11:34:07 Bucky pmxcfs[1702]: [status] notice: members: 1/22496, 2/28978, 3/1717, 4/1702, 5/1688
Aug 28 11:34:07 Bucky pmxcfs[1702]: [status] notice: starting data syncronisation
Aug 28 11:34:07 Bucky corosync[1816]: [QUORUM] Members[5]: 3 4 5 1 2
Aug 28 11:34:07 Bucky corosync[1816]: [MAIN ] Completed service synchronization, ready to provide service.
Aug 28 11:34:07 Bucky pmxcfs[1702]: [dcdb] notice: received sync request (epoch 1/22496/0000000D)
Aug 28 11:34:07 Bucky pmxcfs[1702]: [status] notice: received sync request (epoch 1/22496/00000009)