Dell EMC PowerVault MD 34XX/38XX Series Storage Arrays Administrator's Guide

A consistency group is made up of simultaneous snapshots of multiple virtual disks. Each virtual disk that belongs to a consistency group is referred to as a member virtual disk. When you add a virtual disk to a consistency group, the system automatically creates a new snapshot group that corresponds to this member virtual disk. A consistency group repository must be created for each member virtual disk in a consistency group in order to save data for all snapshot images in the group.

A consistency group snapshot image comprises multiple snapshot virtual disks. Its purpose is to provide host access to a snapshot image that has been taken for each member virtual disk at the same moment in time. A consistency group snapshot image is not directly read or write accessible to hosts; it is used only to save the data captured from the base virtual disk. The consistency group snapshot virtual disk can be designated as either read-only or read-write. Read-write consistency group snapshot virtual disks require a repository for each member virtual disk in order to save any subsequent modifications made by the host application to the base virtual disk without affecting the referenced snapshot image. Each member repository is created when the consistency group snapshot virtual disk is created.