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When you use DFSMShsm, you still use DFSMSdss as the data mover. You can
specify this using the DFSMShsm SETSYS command:
SETSYS DATAMOVER(DSS)
The DFSMS processing at the start of backup is dependent on the DFSMS release
level. For releases before DFSMS 1.2, DFSMSdss first checks the BWO attributes in
the ICF catalog to see if the data set is eligible for BWO. If it is, the backup is
made without attempting to obtain exclusive control and serialize updates to this
data set.
For DFSMS 1.2 onward, DFSMSdss first tries to obtain exclusive control of the data
set. If DFSMSdss succeeds, an enqueued form of backup takes place. If this
serialization fails, DFSMSdss checks the BWO attributes in the ICF catalog to see if
the data set is eligible for BWO. If it is, a BWO backup is attempted. If it is not
eligible, the backup attempt fails.
This change will prevent DFSMS starting a BWO backup after CICS has
abnormally terminated.
At the end of the BWO backup, DFDSS again checks the BWO attributes. If the
data set is no longer eligible for BWO, the backup is discarded. Events that cause
this situation are:
v File closing during BWO, which sets the ‘BWO disabled’ state
v Start of VSAM split, which sets the ‘BWO enabled and VSAM split in progress’
state
v End of VSAM split, which sets the ‘BWO enabled/disabled and VSAM split
occurred’ state.
At the start of a backup, if the state is ‘BWO enabled and VSAM split occurred’,
DFSMSdss resets the state to ‘BWO enabled’. Then, if another VSAM split occurs,
the backup will be discarded at the end of the backup operation.
VSAM access method services
DFSMS access method services import and export operations do not support BWO
in releases earlier than DFSMS 1.2. Access method services always serializes the
data set before exporting it; and when the IMPORT function is used, the BWO
attributes in the ICF catalog are not updated.
For DFSMS 1.2 onward, access method services supports the import and export of
BWO attributes.
Invalid state changes for BWO attributes
CICS, DFSMSdfp, DFSMSdss, and an SMSVSAM server can all update the BWO
attributes in the ICF catalog.
To prevent errors, DFSMSdss fails a BWO backup if one of the following state
changes is attempted during the backup:
v From ‘BWO enabled and VSAM split in progress’ 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, a VSAM split occurs and sets
the ‘BWO enabled and VSAM split in progress’ state.
214 CICS TS for z/OS 4.1: Recovery and Restart Guide