Metro Mirror and Global Mirror partnerships

Metro Mirror and Global Mirror partnerships define an association between a local cluster and a remote cluster.

Before a Metro Mirror or Global Mirror relationship or consistency group can be created with a remote cluster, a partnership between the two clusters must be established. If Global Mirror or Metro Mirror relationships or consistency groups exist between two remote clusters, those clusters must maintain their partnership. Each cluster can maintain up to three partnerships, and each partnership can be with a single remote cluster. As many as four clusters can be directly associated with each other.

SAN Volume Controller clusters also become indirectly associated with each other through partnerships. If two clusters each have a partnership with a third cluster, those two clusters are indirectly associated. A maximum of four clusters can be directly or indirectly associated.

SAN Volume Controller nodes must know not only about the relationship between the two VDisks but also about an association among clusters. A maximum of four clusters can be connected either directly or indirectly.

The following examples show possible partnerships that can be established among SAN Volume Controller clusters.

Figure 1. Two clusters with no partnerships

This figure depicts two clusters that are not in a partnership.

Figure 2. Two clusters with one partnership.

This figure depicts two clusters with one partnership.

Figure 3. Four clusters in a partnership. Cluster A might be a disaster recovery site.

This figure depicts four clusters in a partnership.

Figure 4. Three clusters in a migration situation. Data Center B is migrating to C. Cluster A is host production, and Cluster B and Cluster C are disaster recovery.

This figure depicts four clusters in a migration situation.

Figure 5. Clusters in a fully connected mesh configuration. Every cluster has a partnership to each of the three other clusters.

This figure depicts clusters that are in a fully connected mesh configuration.

Figure 6. Four clusters in three partnerships.

This figure depicts four clusters in three partnerships.

Figure 7 depicts a cluster configuration that is not supported. Five clusters are in the connected set, even though no individual cluster is in more than two partnerships.

Figure 7. An unsupported cluster configuration.

This figure depicts a cluster configuration that is not supported. Five clusters are in the connected set.

To establish a Metro Mirror and Global Mirror partnership between two clusters, you must run the svctask mkpartnership command from both clusters. For example, to establish a partnership between clusterA and clusterB, you must run the svctask mkpartnership command from clusterA and specify clusterB as the remote cluster. At this point the partnership is partially configured and is sometimes described as one-way communication. Next, you must run the svctask mkpartnership command from clusterB and specify clusterA as the remote cluster. When this command completes, the partnership is fully configured for two-way communication between the clusters. You can also use the SAN Volume Controller Console to create Metro Mirror and Global Mirror partnerships.

The state of the partnership helps determine whether the partnership operates as expected. In addition to being fully configured, a cluster partnership can have the following states:

Partially Configured: Indicates that only one cluster partner is defined from a local or remote cluster to the displayed cluster and is started. For the displayed cluster to be configured fully and to complete the partnership, you must define the cluster partnership from the cluster that is displayed to the corresponding local or remote cluster. You can do this by issuing the mkpartnership command on the local and remote cluster that are in the partnership, or by using the SAN Volume Controller Console to create a partnership on both the local and remote clusters.
Fully Configured: Indicates that the partnership is defined on the local and remote clusters and is started.
Remote Not Present: Indicates that the remote cluster is not present to the partnership.
Partially Configured (Local Stopped): Indicates that the local cluster is only defined to remote cluster and the local cluster is stopped.
Fully Configured (Local Stopped): Indicates that a partnership is defined on both the local and remote clusters and the remote cluster is present, but the local cluster is stopped.
Fully Configured (Remote Stopped): Indicates that a partnership is defined on both the local and remote clusters and the remote cluster is present, but the remote cluster is stopped.
Fully Configured (Local Excluded): Indicates that a partnership is defined between a local and remote cluster; however, the local cluster has been excluded. Usually this state occurs when the fabric link between the two clusters has been compromised by too many fabric errors or slow response times of the cluster partnership. Check the error log for 1720 errors by selecting Service and Maintenance > Analyze Error Log to resolve these errors.
Fully Configured (Remote Excluded): Indicates that a partnership is defined between a local and remote cluster; however, the remote cluster has been excluded. Usually this state occurs when the fabric link between the two clusters has been compromised by too many fabric errors or slow response times of the cluster partnership. Check the error log for 1720 errors by selecting Service and Maintenance > Analyze Error Log to resolve these errors.
Fully Configured (Remote Exceeded): Indicates that a partnership is defined between a local and remote cluster and the remote is available; however, the remote cluster exceeds the number of allowed clusters within a cluster network. The maximum of four clusters can be defined in a network. If the number of clusters exceeds that limit, SAN Volume Controller determines the inactive cluster or clusters by sorting all the clusters by their unique identifier in numerical order. The inactive cluster partner which is not in the top four of the cluster unique identifiers displays Fully Configured (Remote Exceeded).

To change Metro Mirror and Global Mirror partnerships, use the svctask chpartnership command. To delete Metro Mirror and Global Mirror partnerships, use the svctask rmpartnership command.

Attention: Before you run the svctask rmpartnership command, you must remove all relationships and groups that are defined between the two clusters. To display cluster relationships and groups, run the svcinfo lsrcrelationship and svcinfo lsrcconsistgrp commands. To remove the relationships and groups that are defined between the two clusters, run the svctask rmrcrelationship and svctask rmrcconsistgrp commands.

Background copy management

You can control the rate at which the initial background copy from the local cluster to the remote cluster is performed. The bandwidth parameter specifies this rate in whole megabytes per second.