Chapter 5. Host configuration 259
7. Click Close to return to the host view, which now lists your newly created host object, as
shown in Figure 5-72.
Figure 5-72 The hosts view lists the newly created host object
8. Repeat these steps for all of your SAS hosts.
After all of the host objects are created, see Chapter 6, “Volume configuration” on page 287 to
create volumes and map them to the hosts.
5.6 Host Clusters
IBM Spectrum Virtualize software supports host clusters starting with version 7.7.1. A host
cluster is a group of logical host objects that can be managed together. For example, you can
create a volume mapping that is shared by every host in the host cluster. The systems use
internal protocols to manage access to the volumes and ensure consistency of the data. Host
objects that represent hosts can be grouped in a host cluster and share access to volumes.
Volume mappings can either be shared or private. Shared mappings are volume mappings
that are shared among all the hosts that are in a host cluster. When a host cluster is created,
any common volume mappings become shared among all the hosts within the host cluster. If
a mapping is not common, it remains a private mapping for that host only. Private mappings
are mappings that are associated with an individual host.
A host cluster allows a user to create a group of hosts to form a cluster, which is treated as
one single entity, thus allowing multiple hosts to have access to the same set of volumes.
Volumes that are mapped to that host cluster, are assigned to all members of the host cluster
with the same SCSI ID.
By defining a host cluster, the user can map one or more volumes to the host cluster object.
As a result the volume, or set of volumes, in turn gets assigned to each individual host object
that is part of the host cluster and each of the volumes gets mapped with the same SCSI ID to
all the hosts that are part of the host cluster with just one command.
A host cluster is made up of individual hosts, and volumes can also be assigned to individual
hosts that make up the cluster. Even though a host is part of host cluster, volumes can still be
assigned to a particular host in a non-shared manner. A policy can be devised which might
pre-assign a standard set of SCSI IDs for volumes to be assigned to the host cluster, and
another set of SCSI IDs to be used for individual assignments to hosts.
A typical use case is to define a host cluster containing all of the WWPNs belonging to the
hosts that are participating in a host operating system-based cluster, such as IBM
PowerHA®, Microsoft Cluster Server (MSCS) and such.
Note: For example, SCSIs ID 0 - 100 can be used for individual host assignment, and
SCSI IDs higher than 100 can be used for host cluster. By employing such a policy, wanted
volumes will not be shared, and others can be. For example, the boot volume of each host
can be kept private, while data and application volumes can be shared.
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