RDF/IMP and IMPX System Management Manual (RDF 1.3+)

Introducing RDF
Compaq NonStop™ RDF/IMP and IMPX System Management Manual—522204-001
1-25
Online Product Initialization
the same audit to its backup system. To bring the two backup databases into rapid
synchronization, you must perform the following steps:
1. Check the EMS event log on both remote systems after the takeover operations have
finished, examining in each the error message that lists the MAT position of the last
record received by the receiver from its extractor. By comparing this message in
each EMS event log, you can easily identify which backup system received the most
audit.
2. On the backup system that received the least audit, use RDFCOM to execute the
COPYAUDIT command. This command copies all the missing audit from the
system that received the most audit to your present local system—the one that
received the least audit.
3. Still on your same local backup system, use RDFCOM to execute a TAKEOVER
command. When this command completes execution, the databases on both backup
systems will be fully synchronized and logically identical to each other.
Now, you can configure a new RDF environment between the two backup systems, so
that one operates as the primary and the other as the backup system. Then, you can start
your applications on the new primary and have full RDF protection on the backup.
For situations where the backup systems are very far apart when the primary fails, for
example when an Expand line between systems is down for several hours, you must take
steps to ensure that the audit missing from the system with the least audit is still on disk
at the backup system with the most audit. Normally, an RDF purger process purges
image files as soon as it determines that they are no longer needed. For triple
contingency, however, the purger on the system with the most image audit must retain all
files that might be needed for this feature, even if those files are no longer needed in that
purger’s own RDF configuration. To support this need, RDF provides the PURGER
RETAINCOUNT configuration parameter, which lets you specify the number of image
files that should still remain on disk when they are no longer needed. You set
RETAINCOUNT to a value that reflects how far apart you believe your two backup
systems are likely to be, depending on the image file rollover rate expected at your site.
(RETAINCOUNT should always be the same value on both backup systems.)
To achieve this type of protection, it is imperative that you carefully follow the
instructions presented in Section 10, Triple Contingency
.
Online Product Initialization
You can initialize RDF/IMP and IMPX while your applications continue to run. This is
particularly useful for installing new versions of RDF into existing production
environments where you cannot afford to stop your applications even briefly to generate
a TMF shutdown timestamp. It is also useful if you encounter a problem for which you
would like to reinitialize RDF without stopping your applications.
For information about this capability, see Online Product Initialization
and the
INITIALIZE RDF command description.