
I have a spare, new 1Tb Samsung drive I could add. I'm not too bothered about losing the backups as all the client PCs are OK and I can re-backup when the server is fixed.
The problem is fixed! I added the 1Tb drive to the data pool and then used the 'Remove' disk option from the Data storage menu to remove all traces of the faulty 500Gb drive. As I expected, all my backups had disappeared but I was able to recreate them from the clients.
I tested the faulty 500Gb which just threw up continous bad blocks so it is being RMAed back to Samsung. Server running smoothly again.