Run OSPF on all five nodes. One option is Quagga, which provides OSPF and other routing protocols for for various Linux flavors including CentOS.
Running OSPF on the nodes makes each one of them a router, and communications between master and slave will automatically switch to another mid system if the one they are using fails.
Note that the mid systems ...
It's actually the same thing for reboot too. Reboot is a pseudouser. From man last
The pseudo user reboot logs in each time the system is rebooted. Thus last reboot will show a log of all the reboots since the log file was created
Your message file show exactly what I expected: a disk/enclosure continuously aborting commands and resetting. The affected disk seems always to be sdc, so it is probably the culprit.
The obvious action to solve the problem is to replace it. However, I would first try to:
reseat your drive and power/data cables;
swap sdc with another disk (to change SAS ...