HP 9000 and HP Integrity servers with HP-UX versions 11.0,
11iv1, and 11iv2 support HP PVLinks (physical volume links) dynamic
pathing when you add more paths to a volume or when you present
a new volume to a host.
Unlike the IBMMultipath Subsystem Device
Driver (SDD), PVLinks does not balance I/O loads and cannot detect the preferred
paths that are set by the system for each volume. Use SDD, unless you are using a clustered-system environment or a volume
as your boot disk.
During failover processing, PVLinks uses
a simple algorithm: It tries the first path, then the next known
path, until it tries all paths. If all paths are unavailable, the
volume goes offline.
If you use PVLinks, consider the following
requirements:
- When you create a volume group, you must complete the following
actions:
- Specify the primary path that you want the host to use when it
accesses the physical volume that is presented by the system.
This primary path is the only path that can access the physical
volume. The preferred path to the volume that is set by the system
is ignored.
- Ensure that the primary links to the physical volumes and thus,
the load, are balanced over the host bus adapters (HBAs),
the Fibre Channel switches, system nodes, and any other devices.
- When you add alternate paths to the physical volume and extend
a volume group, add the new paths in the preferred order that
you want the host to use if the primary path becomes unavailable.
To avoid unnecessary node failover due to HBA, Fibre Channel link,
or Fibre Channel switch failure, ensure that the first alternate
path that you add is from the same system node as the primary
path.