RDF/IMP, IMPX, and ZLT System Management Manual

Introducing RDF
HP NonStop RDF/IMP, IMPX, and ZLT System Management Manual—524388-002
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Loopback Configuration (Single System)
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.
Loopback Configuration (Single System)
A loopback configuration is one where the primary and backup systems are the same
system. This configuration is of no use in a disaster protection plan, but can be useful
for testing purposes. One set of disks can be replicated to another set of target disks
to provide a copy of the live database. There are two operational considerations
unique to this environment:
•
The updaters operate in transaction mode, which means you should not stop TMF
before stopping RDF.
•
The RDF takeover operation cannot be performed, unless you manually stop the
monitor and extractor processes before issuing the TAKEOVER command.