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DFSMSdfp must now disallow the pending change to ‘BWO enabled’ (and
DFSMSdss must fail the backup) because, if the split did not finish before the
end of the backup, the invalid backup would not be discarded.
v From ‘BWO disabled and VSAM split occurred’ to ‘BWO enabled’. This state
change could be attempted if:
1. At the start of data set backup processing, a request is issued to change the
‘BWO enabled and VSAM split occurred’ state to the ‘BWO enabled’ state.
2. But then, before the ‘BWO enabled’ state is set, CICS closes the last file
opened for update, and the data set becomes ineligible for BWO. CICS sets
the ‘BWO disabled and VSAM split occurred’ state to ensure that the BWO
backup is discarded and that no more BWO backups are taken.
DFSMSdfp must now disallow the pending change to ‘BWO enabled’ (and
DFSMSdss must fail the backup) to prevent the possibility of a BWO backup
being taken during a subsequent batch window.
Data set restore
When a BWO backup copy of a data set is restored, using DFSMShsm RECOVER
or DFSMSdss RESTORE, the data set must be serialized to prevent any updates
during the restore operation.
When the restore is complete, the BWO attributes in the ICF catalog are changed to
a ‘Backup restored by DFSMShsm’ state. CICS cannot open the data set until
forward recovery has been completed successfully.
DFSMSdss also resets the recovery point in the ICF catalog to the value it
contained when the backup was made. This ensures that forward recovery starts at
the correct point. This value should not be used for forward recovery of a
non-BWO backup.
Non-SMS managed storage:
If a BWO backup is restored in storage that is not SMS-managed, the BWO
attributes in the ICF catalog are lost. Thus forward recovery is not possible.
Forward recovery logging
The forward recovery utility uses the forward recovery logs to recover a base
cluster.
To do this, it must know:
v The data set to associate with each record on the logs
v The point from which to start recovery
Data sets
Each data set after-image record on the log is associated with a file name.
However, there might be many files associated with the same data set; therefore,
when a file is opened, the association between the file and the data set is recorded
on the forward recovery log by a tie-up record. This information is also written to
the log of logs. For non-BWO backups, the forward recovery utility uses this tie-up
record to apply the log records to the correct data sets.
When a BWO is taken for a data set opened in RLS mode, DFSMSdss notifies each
CICS region having an open ACB for the data set. On receipt of this notification,
Chapter 18. Backup-while-open (BWO) 215