Hi,
snapmirror: A 32-bit volume cannot be mirrored to a 64-bit volume
That's true for VSM. If QSM is any good for you, then it will work though.
1. Can I create the dest volumes as 32Bit? I mean 16TB is still sufficient for us, if the maximum size of a volume is the only benefit we get from 64bit.
Pretty much yes and yes. In fact a 64-bit aggregate may be slower than a 32-bit one on smaller systems (more metadata needs to be loaded into memory).
2. If I create 32bit volumes can I convert them to 64bit on the fly?
Not now. The word on the street though is that ONTAP 8.1 *may* bring online migration capability.
Regards,
Radek