The options available when you initially add a primary volume to an XRC session include FULLCOPY, QUICKCOPY, and NOCOPY. The choice to use the FULLCOPY or QUICKCOPY options for the synchronization process depends on a number of factors, which are described in Adding a volume with the FULLCOPY or QUICKCOPY option.
The SYNCH and SCSYNCH parameters control the number of synchronization tasks that are initiated simultaneously and the tasks that are allocated over the available SSIDs. These options are global for an SDM. In a heterogeneous environment, it may be necessary to set these options based on one particular configuration.
The main consideration for the synchronization options is the available bandwidth between the primary subsystems and the SDM. Configure the environment to fully use this bandwidth so long as this does not cause performance problems due to the increased read activity on the primary subsystems. Although the SDM halts the synchronization process if under stress, concurrent update activity can still occur. The specified SYNCH and SCSYNCH values also depend on the amount of virtual storage available in the LPAR in which the SDM is running. For each synchronization task that is running, the SDM requires 300 kilobytes of real storage.
Set the SCSYNCH option to the highest value calculated for different disk subsystems (or slightly less than this value) to ensure the fastest overall resynchronization. This will be achieved if the subsystems finish a full synchronization at approximately equal times, or if the subsystems with longer synchronization times are able to use the bandwidth of those that have finished earlier.
Because the throughput of a single task depends on a particular environment, it is best to determine optimum synchronization parameters by experimentation. You can use a method similar to the following: