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.