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

HP NonStop RDF/IMP and IMPX System Management Manual—524388-001
10-1
10 Triple Contingency
The triple contingency feature makes it possible for your applications to continue
running with full RDF protection within minutes after loss of your primary system.
What Is It?
The triple contingency feature is made possible by the ability to replicate to multiple
backup systems. Physically, triple contingency consists of two RDF configurations with
the same primary system but separate backup systems, as follows:
RDF Configuration #1
\A ---------> \B
RDF Configuration #2
\A ---------> \C
Both RDF systems are virtually identical to one another, but one replicates data to the
backup system \B and the other to the backup system \C.
Functionally, the triple contingency feature consists of:
•
A purger configuration parameter, RETAINCOUNT, that prevents the purger
process from purging image trail files that might be needed for triple contingency
recovery.
•
An RDFCOM command, COPYAUDIT, that quickly synchronizes the two backup
databases after loss of the primary system and successful takeovers on the
backup systems.
What’s Required?
You must be running the same release of RDF on all three systems.
All protected data volumes in both RDF environments must be mapped to the Master
Audit Trail (MAT) of the associated primary system.
The two backup systems must have the same hardware configuration.
The two RDF configurations must be configured identically (with a few minor
exceptions, such as the suffix characters specified in the INITIALIZE RDF command).
Note. Replication of network transactions is not supported in conjunction with the triple
contingency feature, nor is the replication of auxilary audit trails.