Beneficial Use of GDPS Copy Once Facility (Experimental Evidence)

Brett

By Dave Heggen

There’s no law that requires GDPS implementations to use the Copy Once Facility for Global Mirror, but in my opinion, there ought to be.

The Copy Once Facility incorporates a simple idea: Copy Once describes a group of volumes without critical data; data that does not need to be continuously copied. An old version of the data on these volumes is sufficient for recovery. The beauty of the Copy Once Facility is that it is largely an act of omission: the volumes in the Copy Once group are suspended and withdrawn from the Global Mirror Session after the initial copies are completed.

An additional feature of Copy Once is that you can periodically refresh the data in the DR Site if you want to. Refresh is only required if volumes move, if volumes are added or deleted, or if data gets resized. Some installations perform a refresh once a quarter as a matter of policy to ensure they have a valid copy of the data.

Some examples of good candidates for Copy Once are volumes that provide Data Set Allocation for data to be overwritten in recovery, volumes for which an old version of the data is just fine in case of recovery, such as my TSO data, and volumes for which only the VOLSER is needed at the recovery site, such as Work/Temp/Sortwk volumes. Continue reading