Creating host clusters

You can use the management GUI or the command-line interface to create a host cluster.

When you create a host cluster, you can specify the hosts to include in the cluster. You can also create an empty host cluster and add hosts later. If you select hosts to add to the host cluster, all of the common private volume mappings for the hosts become shared mappings for the host cluster. However, you can also exclude specific volumes from being shared. The private volume mappings are not shared with any other hosts in the host cluster. A host can be a member of only one host cluster at a time.

With shared mapping, volumes are mapped on a host cluster basis. The volumes are shared by all of the hosts in the host cluster, if there are no Small Computer System Interface (SCSI) LUN conflicts among the hosts. Volumes that contain data that is needed by other hosts are examples of a shared mapping.

Using the management GUI

To create a host cluster, complete these steps:
  1. In the management GUI, select Hosts > Host Clusters.
  2. On the Host Cluster page, select Create Host Cluster.
  3. On the Create Host Cluster page, enter the name of the host cluster that you want to create.
  4. Select the available hosts to include within the host cluster. By default, any volumes that are mapped to all the selected hosts become a shared mapping for the host cluster, which each of the hosts inherit. Any new volume mappings that are added to the host cluster are inherited by each host in the host cluster. You can also choose to create an empty host cluster to add individual hosts later.
  5. Click Next.
  6. If you selected hosts to add to the host cluster, you can exclude specific volumes that are already mapped to these hosts. These volumes are retained as private mappings to the individual hosts in the host cluster but do not become shared mappings for the entire host cluster. New hosts that are added to the host cluster do not inherit these volume mappings. Select any volumes that you want to remain private mappings.
  7. If throttles are configured on any of the selected hosts, the throttles must be removed to be included in the host cluster. Throttles can be applied only to the host cluster and not individual hosts within the cluster. If you choose not to remove the throttles from the host, the host is excluded from the host cluster.
  8. Click Next.
  9. On the Summary page, verify the settings and click Create Host Cluster.
    Note: If you selected hosts with volumes that have SCSI ID conflicts, the system does not add these mappings to the host cluster. A SCSI LUN ID conflict occurs when multiple hosts are mapped to the same volume but with different SCSI IDs. In this case, a shared mapping is not created because the system does not allow a volume to be mapped more than once to the same host. The Summary page lists all volumes that contain conflicts and the system retains these mappings as private mappings to the original hosts.

Using the command-line interface

To create an empty host cluster by using the command-line interface, enter the following command:
mkhostcluster -name name
where name is the name of the new host cluster. To add hosts to the host cluster, you can use the addhostclustermember command.
To create a host cluster with host members, enter the following command:
mkhostcluster -name name -seedfromhost host_id_list | host_name_list
where name is the name of the new host cluster and host_id_list or host_name_list is either the ID or name of the hosts that you are adding to the host cluster. By default any mappings that are associated with the host become shared mappings for all the hosts in the host cluster. If multiple hosts are added, any mappings that are in common among the added hosts become shared mappings. Mappings that are not in common remain private mappings to individual hosts.
To create a host cluster with host members but to exclude a specific volume that is mapped to the host from being shared in the host cluster, enter the following command:
mkhostcluster -name name -seedfromhost host_id_list | host_name_list
 -ignoreseedvolume host_id_list | host_name_list
where name is the name of the new host cluster, host_id_list or host_name_list is either the ID or name of the hosts that you are adding to the host cluster. If you want to exclude volumes from shared mappings for the host cluster, use the -ignoreseedvolume parameter to specify any volumes to remain private mappings. For example, if you have a boot drive on a volume, you can exclude that volume from being shared among all the host members in the cluster.