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 virtual disk (VDisk) or when
you present a new VDisk to a host.
Unlike the IBM® System Storage® Multipath
Subsystem Device Driver (SDD),
PVLinks does not balance I/O loads and is unaware of the preferred
paths that are set by the SAN Volume Controller for
each VDisk. Use SDD,
unless you are using a clustering environment or a VDisk as your boot
disk.
During failover processing, PVLinks uses a simple
algorithm: it tries the first path, then the next known path, and
so on, until it has tried all paths. If all paths are unavailable,
the VDisk goes offline.
If you use PVLinks, consider the following
requirements:
- When you create a volume group, you must perform 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 SAN Volume Controller.
This is the only path that can access the physical volume. The preferred
path to the VDisk that is set by the SAN Volume Controller 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, SAN Volume Controller 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 SAN Volume Controller node as the primary path.