VMWare ESX 5.1 Input/Output Error when copying or deleting a file
TryTryAgain answered the question in a comment. The problem was the bad disks. One of the drives had a few bad sectors that could not be repaired.
We took the drive a data recovery centre and they cloned the drive to a new hard drive with the data as is. After installing it back into the server, and re-installing ESXi, the datastore was back online and the VM was restored. Thankfully, no data loss experienced.