After the initial synchronization is complete, you can change the copy direction (see  Figure 6-12). The ability to change roles is used to facilitate disaster recovery. Attention:  When the direction of the relationship is changed, the roles of the volumes are  altered. A consequence is that the read/write properties are also changed, meaning that  the master volume takes on a secondary role and becomes read-only. A Consistency Group (CG) is a collection of relationships that can be treated as one entity.  This technique is used to preserve write order consistency across a group of volumes that  pertain to one application, for example, a database volume and a database log file volume. After a remote copy relationship is added into a Consistency Group, you cannot manage the  relationship in isolation from the Consistency Group. So, for example, issuing a  stoprcrelationship  command on the stand-alone volume would fail because the system  knows that the relationship is part of a Consistency Group. Note the following points regarding Consistency Groups: GLYPH<SM590000> Each volume relationship can belong to only one Consistency Group.  GLYPH<SM590000> Volume relationships can also be stand-alone, that is, not in any Consistency Group. GLYPH<SM590000> Consistency Groups can also be created and left empty, or can contain one or many  relationships. GLYPH<SM590000> You can create up to 256 Consistency Groups on a system. GLYPH<SM590000> All volume relationships in a Consistency Group must have matching primary and  secondary systems, but they do not need to share I/O groups.  Consistency Groups Chapter 6. Copy services  169 Figure 6-12 Role and direction changes  Role Primary Master volume Auxillary volume Role Secondary Role Secondary Role Primary Copy direction Copy direction