RDF System Management Manual for H-Series RVUs (RDF 1.8)

Figure 17-3 ZLT Configuration With Standby and Backup Systems Located at Separate Sites
If the standby and backup systems are not one and the same, you must remember to set up
remote passwords between the standby and backup systems. You must do so with the same
userid that has control over starting and stopping RDF.
If you lose your primary system due to an unplanned outage, you connect the remote mirrors
to the standby system, and then initiate a takeover operation on the backup system. Before
performing the takeover, RDF reads the remaining audit records from the remote mirrors, and
processes those audit records. Thus, RDF can read absolutely all of the audit records that were
generated on the primary system prior to the system failure, and no committed data is lost.
NOTE: You must connect the remote mirrors to the standby system before starting the RDF
takeover operation; otherwise, the takeover aborts because RDF cannot find the disks you
configured in RDF for remote mirroring. In such a case, you should connect the disks and then
restart the RDF takeover operation.
If you lose the primary system to a disaster and that disaster does not affect the standby and
backup systems, no committed transactions are lost because RDF on the backup system can fetch
all missing audit records from the remote mirrors. If a regional disaster takes down both the
primary and the standby systems, however, you can still resume business on the backup system
but without the ZLT guarantee. Some transactions committed on the primary system might be
lost.
Using CommitHoldMode
The NonStop TMF product includes the CommitHoldMode mode.
Using CommitHoldMode 311