HP NonStop RDF, Руководство по управлению

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When the extractor for the new RDF subsystem running from \B to \A reports an RTD time of
0:00, then you know that extractor has caught up and you can then prepare for another switchover
operation to move your application processing back to \A.
The planned switchover repeats the procedure described above, except that you reverse the roles
of systems \A and \B. After doing so, RDF replication once again occurs from \A to \B.
Using STOP RDF, REVERSE and the REVERSE Trigger
The STOP RDF, REVERSE command is a special operation that helps you streamline a switchover
operation to move your business operations from your primary system to your backup system
because you want to perform maintenance involving only your RDF-protected database and you
do not want to stop TMF. The use of the REVERSE trigger executes the various tasks that you
need to accomplish the switchover. Whereas the discussion immediately above involves stopping
TMF and switching over to the backup system, typically because you want to take down the
primary system for maintenance, you would use the STOP RDF, REVERSE operation if you
wanted to leave your primary system up and just switch your business operations involving
your RDF-protected database to your backup system. For this operation to work correctly, you
must execute the following steps:
1. On the primary system, stop the applications that are updating your RDF-protected database.
This is imperative.
2. Watch for the extractor's RTD to be 0:00.
3. Enter the STOP RDF, REVERSE command.
When the extractor receives notice of the operation, it notes where it is in the audit trail and shuts
down, and the updaters shut down as soon as they have reached the equivalent location. This
is identical to the DRAIN command.
Next, RDF automatically executes the REVERSE trigger that you have configured. You would
want this trigger to accomplish the same types of actions as the TAKEOVER trigger discussed
further below in #9 in the section
“How to Plan for the Fastest Movement of Business Operations
to Your Backup System After Takeover” (page 144) . Unlike with the TAKEOVER trigger, you
would want to include in the REVERSE trigger the RDFCOM commands to configure a new
RDF subsystem to run from your former backup system to your former primary system and then
start that subsystem.
CAUTION: If you fail to stop the application associated with your RDF subsystem in step 1,
the probability is high that you will corrupt your backup database. Then, if the REVERSE trigger
moves application processing to the backup system and update activity is replicated by RDF
back to the original primary system, you may find it very difficult to bring the two databases
back into synchronization without loss of committed data.
For further information about the STOP RDF, REVERSE command and the REVERSE trigger,
see the corresponding sections in
“Entering RDFCOM Commands” (page 187) .
Reciprocal Configurations and Switchover
In a reciprocal RDF configuration, two systems act both as a primary and as the backup to the
other.
Carrying Out a Planned Switchover 137