If a shadow set is HBMM-enabled and is actively
using HBMM, then the SET SHADOW/DEMAND_MERGE DSAn: command causes a minimerge operation to occur.
To force a full merge instead of a minimerge operation, you must disable
HBMM on the shadow set before issuing the SET SHADOW/DEMAND_MERGE
DSAn: command. For information about
disabling HBMM, see “How to Disable HBMM on a Shadow Set”
The /DEMAND_MERGE qualifier of the SET
SHADOW command is used primarily to force a merge operation
on shadow sets that are created with the INITIALIZE/SHADOW command
without specifying the /ERASE qualifier. The /DEMAND_MERGE qualifier
ensures that all blocks on the shadow set are the same, including
those blocks that are not currently allocated to files. System managers
can use this command at their convenience during off-peak demands
on their computing environment.
If the /ERASE qualifier is not used when the shadow
set is created with the INITIALIZE/SHADOW command, and the SET SHADOW/DEMAND_MERGE DSAn: command
is not executed, then the overhead of a full merge operation on this
shadow set is even higher than is normally encountered after a system
failure.
System managers can also use the SET
SHADOW/DEMAND_MERGE DSAn: command for
the following reasons:
If the ANALYZE/DISK/SHADOW
command finds differences between the members of the shadow set.
If they want to measure
the impact that a minimerge or a full merge has on their I/O throughput.
