The general recommendation is to use the IPL Method as stated above.
This protects all time stamp dependent operations on your system as
well as BRMS. However, if this is not possible due to operation schedules,
you must carefully plan your BRMS activities so that only the system
that owns a piece of media will try to update it during the time that
system clocks are not yet all reset and the hour is being repeated.
Notes:
Do not perform any BRMS activities during the period of resetting
clocks, and during the one hour of repeated time. If you must start
backups during the repeated hour, ensure that the system owns enough
scratch media for the backups, and that no other update operation
will occur on that media during the repeated time period.
If you repeat a period of time by setting the clocks backwards,
and during that period, you cause the same volume to be updated, those
updates might not be synchronized correctly. BRMS relies upon time
stamps on the records to order the records in the file and decide
if an update should occur or not.
Save jobs will synchronize an update to the volume information
about all network systems to show that the volume is active and owned
by the saving system. If one of the other systems had a record for
that volume that appeared to be more recent (because that system did
not yet have its clock reset), that system would throw away the update
record, and synchronize its view of the volume to the other network
systems, causing an otherwise valid update to be ignored. It would
be possible for BRMS to then overwrite such a tape, and the integrity
of your system recovery plan would be compromised.
On the day that times will be changed, you should ensure that
while you are doing your nightly saves, no other update activity is
occurring for the same volume on another system. The best way to avoid
this is to ensure that you have sufficient expired media owned by
each system for the backups during this time change period (so that
systems will not try to 'borrow' another system's media). Also make
sure maintenance, movement, WRKMEDBRM opt 2, and all other update
activity do not occur. That way, updates to media records will only
be initiated by save activities from systems which already own the
volumes.