[Samba] PDC and BDC: how to sync profiles

[Andreas]

I was wondering how people sync the roaming profiles in an environment
with a PDC and multiple BDCs. Are profiles better stored in another
server (a member server) instead of the xDC?

I could use rsync from the PDC to the BDC, but that doesn't work the
other way around, i.e., when a user logs in via a BDC whatever changes
they make won't go back to the PDC. Unless the profile is:
- always stored in the PDC
- stored elsewhere (i.e., not a xDC)

Seems it's better to store the profiles in a single server and live with
it when that server goes down for some reason or another. Or not? What
do people usually do?