RDF/IMP and IMPX System Management Manual (RDF 1.4+)

Introducing RDF
HP NonStop RDF/IMP and IMPX System Management Manual—524388-001
1-7
Features
Features
In providing backup protection for online databases, RDF offers many advantages:
•
Continuous Availability
RDF maintains an online copy of your production database on
one or more backup systems. If the primary system should go down, the backup
database(s) will be consistent and you can resume your business processing on a
backup system with minimal interruption and data loss.
•
Fault tolerance
You can restart RDF after a system crash. Single processor failures do not bring
the subsystem down. If a double processor failure occurs, RDF goes down, but it is
restartable (issue a START RDF command after the processors have been
restored).
•
Flexibility in protection
You can run RDF with updating on the backup system either enabled or disabled.
RDF is also very flexible with regard to system interrelationships and to disk usage
requirements on backup systems. Besides the most basic configuration of a single
primary system protected by a single backup system, you can have any of the
following (see Figure 1-2, RDF Topologies):
•
Multiple primary systems protected by one backup system.
•
Reciprocal protection between two systems, where each is the backup to the
other (different databases on the two systems).
•
A single primary system whose database changes are replicated to databases
on multiple backup systems. Such an environment makes possible
simultaneous read-only access to all of the backup databases (this is desirable
for query-intensive applications such as telephone directory assistance).
•
Triple contingency—a special instance of the database replication feature
whereby a single primary system is protected by two identical backup systems.
This feature allows your applications to resume, with full RDF protection, within
minutes after the loss of your primary system, provided the two backup
systems are not too far behind.
RDF does not require an identical one-to-one volume relationship between
volumes on the primary system and those on the backup system. Backup volume
names do not have to match primary volume names. The subsystem can direct
audit information from more than one audited volume on the primary system to a
single volume on the backup system, provided that no more than one partition of a
file exits on any backup volume. (For information on partitioned files, see the
Guardian User’s Guide.)