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Dell EMC Metro node 7.0.1 Administrator Guide

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Visibility

Visibility controls which clusters know about a consistency group.

NOTE:Visibility for consistency groups differs from the visibility property for devices. Devices can have visibility set to local (visible only to the local cluster) or global (visible to both clusters). All distributed devices have global visibility.

By default, a consistency groups’s visibility property is set only to the cluster where the consistency group was created. If a consistency group is created on cluster-2, it is initially visible only on cluster-2.

The visibility of the volumes within the consistency group must match the visibility of the consistency group.

If the visibility of a volume in a consistency group is set to local, the visibility of the consistency group cannot be set to include other clusters. For example, if volume LocalVolume with visibility property set to local is added to consistency group TestCG the visibility of TestCG cannot be modified to include other clusters.

In general, visibility is set to one of three options:

  • Configure the consistency group to contain only volumes that are local to the local cluster.
  • Configure the consistency group to contain only volumes that have storage at one cluster, but have global visibility.
  • Configure the consistency group to contain only volumes that are distributed with legs at both clusters.

When a consistency group’s visibility is set to a cluster, the consistency group appears below /clusters/cluster-n/consistency-groups context for the cluster.

NOTE:The context for a specified consistency group appears in a cluster’s consistency group CLI context only if the Visibility property of the consistency group includes that cluster.

Under normal operations, the visibility property can be modified to expand from one cluster to both clusters.

Use the set command in /clusters/cluster/consistency-groups/consistency-group context to modify the visibility property. If consistency group TestCG is visible only at cluster-1, use the set command to make it visible to cluster-1 and cluster-2: 

VPlexcli:/clusters/cluster-1/consistency-groups/TestCG> set visibility cluster-1,cluster-2

If a consistency group contains virtual volumes with a given visibility (for example, a member volume’s visibility is local), the visibility property for the consistency group cannot be changed to conflict with the visibility property of the member virtual volume.

For example, consistency group TestCG is visible only at cluster-1, and contains a volume V whose device is at cluster-1 and has local visibility. Both the following commands will fail, because the volume V is not visible at cluster-2. 

VPlexcli:/clusters/cluster-1/consistency-groups/TestCG> set visibility cluster-1,cluster-2
VPlexcli:/clusters/cluster-1/consistency-groups/TestCG> set visibility cluster-2

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