Gluster volumes are not started automatically on boot.

If you got two node cluster and one of the node is down and other is rebooted, the daemons wouldn't get started until and unless there is no peer in the cluster or at least a friend update (happens during handshake) is received. This is to ensure the node doesn't spawn daemons with having stale data as it was down. In this case the node will never receive a friend update as the other only node in the cluster is down.

'gluster volume start force' can bypass this check and can start the daemons, but consistency is not guaranteed.