Error: Failed to initiate a backup or restore for a virtual machine. Probable cause is the datastore for the virtual machine is not accessible
In order to try and resolve the issue I change the DNS server back to the original DC and rebooted. I really didn't think this caused the initial issue but it was the only thing that had changed. As expected, this didn't resolve the issue. When searching for the resolution I did come across this KB article which asks you to verify that all datastores are actually associated with hosts but this did not resolve my issue. I finally tried rebooting the hosts to see if this resolved and also re-creating the backup job but no success.
After following Cormac Hogans (Blog | Twitter) excellent article I realised that there were no log files available from the date the issue started happening which was Thursday 3rd April (Last successful backup was on the 2nd April)
So, I guess what I'm really asking now is has anyone else seen this issue or can anyone point me in a direction to start investigation?
Update - 7/04/2014
After searching through various log files and google I did find this article which shows an error message that I was seeing in one of the log files. The resolution was to stop and start the MCS service with the following commands via an SSH session:
dpnctl stop mcs
dpnctl start mcs
After doing this the backups still failed but I then gave the appliance another reboot and it looks like that might have resolved it. A backup of an individual machine is currently running so I'll see what happens tomorrow morning
Update - 8/04/2014
All backups have completed successfully last night so looks like the fix above has worked.