Originally Posted by Dreaming 
Hmm, I couldn't run the diagnostics tool, because WD diagnosis tool saw the array as just one single drive (and then said the cable wasnt plugged in). Not much use there. I'll see what else they've got on their website.
No problem, most of these hard disk diagnostic tools have difficulty seeing through a RAID array.
All you have to do is temporarily disable RAID in the BIOS of your motherboard. Scan the drive with the diagnostic tool, and then re-enable RAID before restarting your OS. You won't lose the array as a result of temporarily disabling it like this.
However, as far as the risk of data loss is concerned, if the drive concerned is on a RAID 0 array, you're gonna lose the data if the drive does need replacement anyway. As such, well worth thinking ahead to your method of backup now.