DFS includes two administrative databases: the Fileset Location Database (FLDB) and the Backup Database. You can increase system efficiency, file availability, and system reliability by replicating (copying) these two databases on multiple server machines. If one machine housing a copy of a database then becomes unavailable, the information can still be accessed from a copy of the database on another machine.
Unlike replicated filesets, replicated databases may change frequently. To ensure consistent system behavior, all copies of a database must be identical. DFS uses a library of utilities, Ubik, as a mechanism for synchronizing multiple copies of a replicated database. (Because Ubik is a subroutine library, it does not appear in listings of the processes running on a server machine.)
In DFS, one server machine houses a master copy of a replicated database such as the FLDB. When a user alters information in the database, Ubik coordinates the distribution of the change from the master copy to the copies of the database on other machines; the distribution is automatic and nearly instantaneous. Ubik dynamically selects a master copy of a database from among the servers that house it. The selection process and the propagation of changes to all copies of a database are managed entirely by Ubik and are transparent to administrators and users.
More:
Providing Information for Ubik
Configuring Database Server Machines for Ubik