You can adjust the cycling period by using the  chrcrelationship -cycleperiodseconds  < 60 - 86400 >  command from the CLI. The default value is 300 seconds. If a copy does not  complete in the cycle period, the next cycle does not start until the prior cycle completes. For  this reason, the use of Change Volumes gives you the following possibilities for RPO:  Carefully consider your business requirements versus the performance of Global Mirror with  Change Volumes. Global Mirror with Change Volumes increases the intercluster traffic for  more frequent cycling periods. Therefore, selecting the shortest cycle periods possible is not  always the answer. In most cases, the default must meet requirements and perform well. Important:  When you create your Global Mirror Volumes with Change Volumes, ensure  that you remember to select the change volume on the auxiliary (target) site. Failure to do  so leaves you exposed during a resynchronization operation. For the best performance, MM/GM volumes must have their preferred nodes evenly  distributed among the nodes of the systems. Each volume within an I/O Group has a  preferred node property that can be used to balance the I/O load between nodes in that  group. MM/GM also uses this property to route I/O between systems. If this preferred practice is not maintained, such as if source volumes are assigned to only  one node in the I/O group, you can change the preferred node for each volume to distribute  volumes evenly between the nodes. You can also change the preferred node for volumes that  are in a remote copy relationship without affecting the host I/O to a particular volume.  The remote copy relationship type does not matter. The remote copy relationship type can be  Metro Mirror, Global Mirror, or Global Mirror with Change Volumes. You can change the  preferred node both to the source and target volumes that are participating in the remote copy  relationship. The background copy performance is subject to sufficient RAID controller bandwidth.  Performance is also subject to other potential bottlenecks, such as the intercluster fabric, and  possible contention from host I/O for the IBM Spectrum Virtualize system bandwidth  resources. Background copy I/O is scheduled to avoid bursts of activity that might have an adverse effect  on system behavior. An entire grain of tracks on one volume is processed at around the same  time, but not as a single I/O. Double buffering is used to try to use sequential performance  within a grain. However, the next grain within the volume might not be scheduled for some  time. Multiple grains might be copied simultaneously, and might be enough to satisfy the  requested rate, unless the available resources cannot sustain the requested rate. Global Mirror paces the rate at which background copy is performed by the appropriate  relationships. Background copy occurs on relationships that are in the  InconsistentCopying state with a status of  Online . Chapter 11. Advanced Copy Services  557 11.6.15 Background copy performance 11.6.14 Distribution of work among nodes GLYPH<SM590000> If your replication completes in the cycling period, your RPO is twice the cycling period. GLYPH<SM590000> If your replication does not complete within the cycling period, RPO is twice the completion  time. The next cycling period starts immediately after the prior cycling period is finished.