If the 10K.2 drives and the 10K.3 drives are in the same storage pool, that could also be contributing.
The stale drive can be ejected. The RAID should be rebuilding from everything except that drive, so it shouldn't be in use at all.
I think you might have the older I/O fan module. Can you also check if your power supplies are D73299-008 or higher? both of those hardware parts had a higher RVI than the newer ones.