Freeing subsystem resources

Performing a physical copy of the data uses subsystem resources and can impact the performance of other I/O operations that are issued to the ESS. Using the FCNOCOPY keyword on a DFSMSdss copy command prevents the ESS subsystem from performing a physical copy of the data. However, when you designate the FCNOCOPY keyword, you must either withdraw the FlashCopy® relationship when you no longer need the copy or convert the existing FlashCopy relationship from FCNOCOPY to COPY mode.

Withdrawing the FlashCopy relationship frees the subsystem resources that are used to maintain the FlashCopy relationship. You can withdraw the FlashCopy relationship by:

Performing a full volume dump of the target volume, specifying the FCWITHDRAW keyword on the DUMP command.
Entering the TSO FCWITHDR command.

DFSMSdss also issues an FCWITHDRAW with the Delete Data Space Withdraw (DDSW) option to the target volume during COPY and RESTORE commands using FULL and TRACKS operations.

When an existing FlashCopy relationship is converted from no-background copy (FCNOCOPY) to background copy mode, the relationship ends (unless the relationship is persistent) when the background copy has completed. When the relationship ends, it frees the subsystem resources that are used to maintain the FlashCopy relationship. You can change the existing FlashCopy copy mode by performing a physical full volume or tracks copy specifying the FCNOCOPYTOCOPY keyword along with the source volume or extents for which you want background copy to be started. The FCNOCOPYTOCOPY function will initiate background copy of any NOCOPY FlashCopy relationships in which the specified source volume or extents are participating.

In general, if you want a temporary copy of the data, specify FCNOCOPY and then withdraw the FlashCopy relationship when you no longer need the copy. If you want a permanent copy, but want to delay background copy until a convenient time, specify FCNOCOPY to get a point-in-time copy and then perform FCNOCOPYTOCOPY later to start background copy. If you want a permanent copy and do not want to delay background copy, do not specify FCNOCOPY. Allow the ESS subsystem to perform the physical copy and release the subsystem resources that are used to maintain the FlashCopy relationship.

Note: A Persistent FlashCopy relationship does not end when physical background copy has completed. The relationship can be removed by performing a Withdraw FlashCopy operation (e.g., TSO FCWITHDR command). An Incremental FlashCopy relationship is an example of a Persistent FlashCopy relationship supported by DFSMSdss. If you want to establish a Persistent FlashCopy relationship independent of Incremental FlashCopy, you can use the ESS Copy Services Web User Interface.

For more information about using the SETSMS command, refer toz/OS MVS System Commands.

For more information, refer to FCNOCOPY, FCNOCOPYTOCOPY, and FCWITHDRAW.