Introduction to Data Management

Protecting Databases With RDF
8-2 15873 Tandem Computers Incorporated
Figure 8-1. RDF in Operation
S8020-028
Backup
Database
RDF
RDF
TMF Audit
Trail
Dynamic
Database
Update
TMF
Audit Trail
Buffer
Primary
Database
\NODEA \NODEB
Receive Audit
Store Audit
for Update
Dynamic Extract
and Transmit
Audit Trail
If the primary system is shut down by a disaster, the backup system becomes the
primary processing site for the applications that were using the primary database.
Operators at the backup site start copies of the application processes on their system
and switch communications lines so that terminals processing the applications are
connected to the backup system.
By fully supporting application and database recovery, RDF can serve as the
cornerstone of a successful business resumption plan for your critical online
applications.
To maintain the backup database, RDF runs on both the primary and backup systems.
On the primary system, RDF monitors and extracts information from TMF audit files
and sends this information over the EXPAND network to the backup system. On the
backup system, RDF receives the audited transactions and stores them in disk buffers.
RDF then applies these transactions to the database, maintaining a duplicate of the
primary database. This backup database is usually current within seconds of the
primary database.
Updating activities on the duplicate database can be temporarily suspended without
compromising the integrity of the online backup process. The audit transactions
accumulate in the RDF disk buffers at the backup site until the updating is resumed.
Then, all accumulated updates are automatically applied in the correct sequence.