Thanks for the tips
"Bit late to say backup isn't it?" - this was the point of putting RAID in place. Mirroring seemed an appropriate solution for around 50Gb of data. Unfortunately it would probably have been alright if I hadn't....
Not sure why it decided to resync - I deliberately steered clear of the other RAID configurations as mirroring seemed the safest bet.
I use the drive to archive digital photos - so there are only JPEG files on the drive. I will check for any other file types that may have found their way onto the drives and see what state they are in though.
My though was to try and disconnect each drive to see if one individually had good files on it. If Adaptec cannot come up with any suggestions I will try the check disk option first. Another option is to force the array to resync again - but I am wary of making the situation even worse.
Will post again with any progress.