[Samba] LDAP master-slave and BDC ?

[Msdigital]

I am a bit confused, about the LDAP master-slave and BDC. I have an Samba-LDAP server that serves as my PDC. All my users authenticate to this server. I would like to set up a BDC for failover. What is the difference between a BDC and a LDAP Slave server?

Second part.

Does anyone on this list have this type of configuration, PDC-BDC or Master/Slave and can help do the same?

-Thank you

Mark