Instruction manual

CHAPTER 8. SYSTEM BACKUP FOR DEFINITY G3r
Command Operation
The save translation command writes two time-stamped identical copies of translation data to
the selected device(s). The time stamp for both copies will be the same (it will be the time of writ-
ing to the first copy). Each copy is written as consecutive 2K blocks. Each block contains a
checksum for error detection purposes. Each copy contains a time stamp and the state of the
copy (either “good” or “bad”).
The save operation writes one complete copy first; then writes the second copy in a different area
of the device. The save operation updates only one copy at a time. The save operation will
always choose to overwrite the “least good” copy first. The following selection criteria should be
applied on both the active and standby devices:
● If a copy has a bad status, always overwrite that copy first.
● If both copies have good status, overwrite the one with the older time stamp. If both time
stamps are the same, it does not matter which copy is overwritten first since the copies
are identical.
Each copy of the translation data is marked “bad” prior to a translation save operation, and it will
only be marked “good’ after the save operation to that file completes successfully. Any failure
during the save operation, including a system crash, will usually affect only one copy of transit-
ion data. If this occurs, the affected copy will be marked with a “bad” status indicator and should
not be used to bad translation into the system. Thus an intact copy of translation can be used as
a backup. Normally at least one of the two copies will be in a good state. If save translation is
performed automatically as part of daily scheduled maintenance, there is a high degree of prob-
ability that identical copies of translation exist on the tape.
When MSS devices on both
processors in a duplicated system are specified, the save operation
will save translation data from the active processor to the active and standby MSS devices in
parallel. The status of each save operation is reported to the user separately. If one of the save
operations fail, the save operation to the other device continues.
If invoked during regularly scheduled maintenance, the
save translation command in a dupli-
cated processor system will save the translation to one of the MSS devices even if the other dev -
ice is out of service.
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