RDF System Management Manual

Zero Lost Transactions (ZLT)
HP NonStop RDF System Management Manual—524388-003
16-5
Using CommitHoldMode
all of the audit records that were generated on the primary system prior to the system
failure, and no committed data is lost.
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 may be lost).
Using CommitHoldMode
Starting with the G06.26 release version update (RVU), the HP NonStop TMF product
includes the CommitHoldMode mode.
If you want ZLT protection, you must configure your audit trails with the
COMMITHOLDMODE attribute set to on. Doing so causes each write to the audit trail
to be directed to the remote audit-trail disk first. If that write fails for any reason, TMF
activates commit-hold mode.
If CommitHoldMode mode is activated, TMF stops all further commit operations.
Because transactions on the primary system cannot commit or abort while the remote
mirror is unavailable, you achieve ZLT protection if you should lose your primary
system while commit-hold mode is activated. However, when such an event occurs,
transaction processing on the primary system effectively stops.
TMF provides another configuration attribute associated with CommitHoldMode:
COMMITHOLDTIMER. If CommitHoldMode is activated, the COMMITHOLDTIMER
value specifies how long you want CommitHoldMode to remain activated and what to
do when that time is reached. The parameters are as follows:
COMMITHOLDTIMER {timeout [ON TIMEOUT {SUSPEND|CRASH}] | -1 }
If timeout is set to a positive value (from 5 seconds to 24 hours) and
CommitHoldMode becomes activated, all commit processing stops until either you
correct the issue causing the activation or the timeout value is reached. If the timeout
value is reached, TMF performs the action specified by the ON TIMEOUT option
(SUSPEND or CRASH).
CommitHoldMode affects transaction processing on your primary system dramatically
when a remote mirror becomes unavailable. If a remote mirror becomes unavailable,
you must choose whether you need ZLT protection or the resumption of transaction
processing.
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.