HP StorageWorks SAN Virtualization Services Platform Manager User Guide (5697-0454, May 2010)

10 Working with hosts
A host is connected to two DPMs in a DPM group using a dual-fabric SAN. Each host requires operating
system specific multipath software to perform the necessary path management. A host that is connected
to the fabric through two DPMs requires operating system–specific multipath software, available from
HP, to perform path management and, if supported by the multipath driver, load balancing.
DPMs report information about the host bus adapters (HBAs) through which they communicate with
hosts. The active VSM server detects each host’s HBAs through the DPMs. The VSM server creates a
separate host entity to represent each HBA that is detected but not yet registered with a host. To
register multiple HBAs on a host as belonging to a single host, a user must define the host. A host
defined this way is called a user defined host (UDH).
Hosts can be connected to multiple SVSP domains and can be assigned virtual disks, and other VSM
storage elements composed of virtual disks, such as snapshots or virtual disk groups (VDGs) from
multiple SVSP domains. A host communicates with the domain through the DPMs, and the DPMs
present virtual disks to the host as LUNs. The LUN range used to present virtual disks to the host is
configurable. By setting different LUN ranges for a host per SVSP domain, you prevent a possible
conflict in which the host is requested to present different virtual disks, from different domains, with
the same LUN number.
You can control which DPM in a DPM group presents virtual disks to the host. There are three ways
in which the DPM can be determined:
• According to VSM’s static load balancing policy. This is the default. VSM distributes virtual disks
evenly between DPMs for static load balancing. The first virtual disk that is assigned permission
to the host is presented by the first DPM in the group. The next virtual disk is presented by the
second DPM that supports the configuration, and so on. When you assign host permission to a
VDG, all members of the VDG are assigned to use the same DPM. All subsequent virtual disks
assigned permission to the host are assigned to the other DPM, until both DPMs service the same
number of virtual disks.
• According to a user-defined path preference for all virtual disks assigned to the host. You can
optionally set a preferred path for the host. This preferred path overrides the even distribution of
virtual disk assignments, setting a primary DPM to present all virtual disks to the host.
• On a per virtual disk basis. You can optionally specify a primary and a secondary DPM for
presenting the virtual disk to the permitted host. This setting overrides the preferred path set for
the host. For information about specifying primary and secondary DPMs per virtual disk, see
“Managing Data Path Modules” on page 118.
You can:
• View the supported operating systems and personalities (view the host operating systems supported
by VSM and the operating systems' supported personalities)
• View the hosts list (view all hosts registered to the SVSP domain)
• View host information (view information about each host in the tabs area)
• Define hosts (create a UDH to register a host)
• Change UDH operating system (change the operating system configured for a UDH)
• Change host personality (change the personality of a UDH)
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