I'm about to put a pair of 16TB units online. Each has three 3ware H/W RAIDs.
2x4.5 TB and 1x6.2TB
Created a VG using one 4.5 and 1 6.2 Keeping the last 4.5TB as expansion space.

I'll be using these as a NAS pair right now.

Half the users will be mapped to unit 1 with data replication to unit2 and the other half mapped to unit2 with data replicated on unit1.

So I get some load balancing and hot backup as well. Should one unit have a disastrous failure I just map those users over to unit2 & allow access.

Now my question.

Is there any reason I shouldn't create a single 10+ TB LV?