Drive failure on my LaCie 2Big (possibly gone wrong!)

One of the drives on my LaCie 2Big (in RAID-1 configuration) has stopped working, LaCie reckon it's either a drive failure or a failure in the RAID controller.

Interesting dilemma now - do I return the unit to the supplier (not LaCie direct) for them to either wipe or replace it under supplier warranty, or do I fork out for (or push the supplier for) sending a replacement hard-drive to me so that the RAID-1 can do it's thing, re-sync the new disk with the remaining good one, and not wipe all the files on what is meant to be my fail-safe drive?

Interesting thing is that it's fail-safe right up to the point where you need to fix the fault under warranty!

Think I'll try to push the supplier to send a replacement disk, but doubt they will.