Well, if you see this and you did nothing to your cluster other than freeing up some space, you may just find yourself seeing the error below,
Stopping cluster: Stopping dlm_controld... [ OK ] Stopping fenced... [ OK ] Stopping cman... [ OK ] Unloading kernel modules... [ OK ] Unmounting configfs... [ OK ] Starting cluster: Checking if cluster has been disabled at boot... [ OK ] Checking Network Manager... [ OK ] Global setup... [ OK ] Loading kernel modules... [ OK ] Mounting configfs... [ OK ] Starting cman... corosync died: Could not read cluster configuration Check cluster logs for details
Google around and you get scary stuff like reinstalling the cluster and stuff like that. But what really works for me without jumping off the building was that the cluster logs in /var/log/cluster was deleted and causes the corosync to die. Hence, you might want to check your log is there before doing some fanciful work of redoing everything.