Thanks for everyones' input.  As usual, this is a great place to get  
technical advice.  A few quick replies...

> Wouldn't JBOD end up setting everything up as a >1300Gb single unit?

Hm.  I'm afraid I may have misunderstood the term.  I thought 'just a  
bunch of disks' meant I'd be able to use the 2 disks separately, like  
they'd be separate logical devices, and a client could mount 1 or the  
other independently.  Reading further, it seems that's not correct.   
Crud.  Looks like JBOD is more like RAID 0 w/o the striping.  I guess  
that's what I get for inferring too much from an acronym. :)

So, in this single enclosure, how do I keep the 2 separate?  Backups  
on the big drive, and extra primary storage on the smaller one?   
Hopefully there will be some options in the enclosure's OS that will  
allow that kind of setup.  Otherwise I'll probably be returning it.

> I'd say to put the backup in a seperate box-- just to isolate it as
> much as possible.  If the power supply in the "external storage" NAS
> goes out in violent fashion, or someone deletes the wrong thing, you
> don't want it also taking the "backup" drive.

This is a good point.  But they want something relatively small.   
Keeping the costs down is another concern.  I think those  
considerations are going to win out.  I can educate them about the  
importance of not using the backup drive for anything aside from  
backups.  (Assuming I can actually keep the 2 drives separate on a  
technical level...)

> www.openfiler.com

Now that is pretty cool.  I think it'd be too complex for the current  
situation, but the next time I need external storage for myself, I  
think I'll check that out.  Thanks!

alex