FlashCopy consistency groups

A consistency group is a container for mappings. You can add many mappings to a consistency group.

The consistency group is specified when the mapping is created. You can also change the consistency group later. When you use a consistency group, you prepare and start that group instead of the individual mappings. This process ensures that a consistent copy is made of all the source volumes. Mappings to control at an individual level are known as stand-alone mappings. Do not place stand-alone mappings into a consistency group because they become controlled as part of that consistency group.

When you copy data from one volume to another, the data might not include all that you need to use the copy. Many applications have data that spans multiple volumes and requires that data integrity is preserved across volumes. For example, the logs for a particular database usually reside on a different volume than the volume that contains the data.

Consistency groups address the problem of applications having related data that spans multiple volumes. In this situation, copy operations must be initiated in a way that preserves data integrity across the multiple volumes. One requirement for preserving the integrity of data that is being written is to ensure that dependent writes are run in the intended sequence of the application.