[Samba] Recommended passdb backend

[Damian Gerow]

We're in the midst of setting up a Samba 3 system as our PDC.  I come from a
Samba 2 world, where the passdb backend was smbpasswd.  What's the ...  er,
'best' passdb backend at this point?

To qualify best, there's no limitations on the type of storage used (LDAP,
MySQL, XML, etc).  I'm just looking for something that's going to make
integration with a 2000/XP domain easier, and is going to be well supported
into the future.

TIA.