You can run DEFRAG and CONSOLIDATE functions on a volume at any time. However, these operations lock the VTOC (through the RESERVE macro) and the VVDS, if it exists on the volume. They also serialize on data sets through ENQ or dynamic allocation. These activities might cause excessive wait time for other jobs to update the VTOC. Therefore, times of low system activity are best for DEFRAG and CONSOLIDATE runs.

DFSMSdss erases the source location for every extent that is moved during the DEFRAG or CONSOLIDATE operation when you specify the ADMINISTRATOR keyword. This occurs even if the extent is not part of an erase-on-scratch data set.

DFSMSdss can use FlashCopy® during a DEFRAG or CONSOLIDATE operation if the device is in an ESS that supports data set FlashCopy. FlashCopy is much faster than traditional data movement methods, especially when you are moving large amounts of data.

DFSMSdss can also use SnapShot to quickly move the data from the source location to the target location during a DEFRAG or CONSOLIDATE operation if the device is in a RAMAC Virtual Array. SnapShot is much faster than traditional methods of data movement, especially when moving large amounts of data.