I realize that you have lesss than 30 GB of music but,
is the MTBF on these disks that high that you need to pay double for storage space ?

To me, twice the storage space and double the MTBF is a way better deal than half the storage space and half the MTBF...
...I mean what's a drive good for these days, a couple years?

So over the course of a couple years, it fails once.
Not such an anconvenience to me, and it's a perfect time for an upgrade.
A couple years after you bough you last drive, the prices will have come way down.

all this is moot though, you have all the space you need, I'm sorry, just my ramblings...

In your setup, you could also put a toggle switch on the back of the empeg that would toggle power to each of your drives, then if one fails, you just flip the toggle, it turns off power supply to one drive and supplies it to the other...