RDF System Management Manual for J-series and H-series RVUs (RDF Update 13)

When the takeover operations are complete, the databases on systems \B and \C are logically
identical to one another, you have not lost any committed data regardless of the number of auxiliary
audit trails involved.
Figure 12 RDFZLT with Triple Contingency
RDF Traffic \A->\B (Expand)
Limited to 100km by Remote Mirrors
Audit Trail Disks
(\A->\B)
Up To 15 Auxiliary Audit Trails
XP Array A XP Array B
Audit Trail
mirrors
$AMAT-P
$AAUX1-P
$AMAT-B
$AAUX1-B
\A (RDF Primary)
RDF Traffic \A->\C
(Expand) Distance Unlimited
ZLT Recovery Traffic
\A->\C via \B (Expand)
Distance Unlimited
Fibre Channel
Controller
\B (RDF Backup)
RDF Standby for
|A->\B and |A->\C
Fibre Channel
Controller
\C (RDF Backup)
This diagram shows two ZLT configurations:
RDF
Instance
\A->\B
\A->\C
\A
\A
\B
\C
\B
\B
Primary
System
Backup
System
Standby
System
Online Continous data traffic
Offfline recovery traffic
Fibre Channel Link continous data
trafiic (Primary disk -> remote mirror)
Summary
To be able to use the triple contingency feature, you must:
1. Establish two RDF configurations with the same primary system and separate backup systems.
2. Ensure that the hardware configurations of the two backup systems are identical with regard
to data volumes and image trail volumes.
3. Ensure that the data volumes and image trails of the two RDF configurations are configured
identically with respect to the two backup systems (with the few minor exceptions noted earlier
in this chapter).
4. Set an adequate purger RETAINCOUNT parameter on the backup systems (it must be the
same on both).
Upon loss of the primary system, you must:
1. Issue a TAKEOVER command on both backup systems.
2. When the takeovers have completed successfully, examine the EMS event log on both backup
systems for a 735 message to determine which system is missing audit records.
Summary 269