HP 3PAR HP-UX Implementation Guide

Total PE 1279
Free PE 1279
Autoswitch On
Proactive Polling On
Setting Up Multipathing Software on HP-UX 11i v2
1. PVLinks, a component of Logical Volume Manager (LVM), can be used with storage server
VVs that are exported on multiple paths to the host server to provide path failure management.
PVLinks is an alternate pathing scheme where a primary and one or more alternate paths are
defined for a device. The primary path is used until it fails, which causes one of the alternate
paths to be used until the primary path is restored. In order for path failover with PVLinks to
work, host I/O must be pointed at the LVM Logical Volume device, not at the raw or block
special files in /dev/rdsk and /dev/dsk.
WARNING! Because HP-UX sees every path to a device (that is, a single storage server
VLUN) as a different device (for example, cxt0d0 and cyt0d0), the potential to overwrite data
on a LUN exists if I/O is performed directly to the /dev/dsk/ or /dev/rdsk/ special files.
The PVLinks feature is part of LVM volume management. See the HP LVM documentation on
the HP SC: HP Support Center for information on using PVLinks. One such reference is:
Managing Systems and Workgroups: A Guide for HP-UX System Administrators HP, 9000,
Computers, Edition 9, Manufacturing Part Number: 2355-90950, Chapter 6: “Administering
a System: Managing Disks and Files,” Section: “Setting Up Alternate Links to a Physical
Volume.”
Alternate links (paths) to a volume are defined at the volume group level using the vgcreate
command or by using the SAM GUI.
# sam > Disk and File systems > Volume Groups & Logical Volumes
The order of failover paths specified during volume creation is important, as the failover priority
will be considered in the same order as used when the volume was created. For example:
# vgcreate <volume name> <path1> <path2> <path3>…<pathn>
The failover path for the primary active path will be increased by 1 up to path n.
NOTE: If you are using the SAM utility to create volume groups, it creates all possible
alternate links by default.
After the primary link has recovered, LVM will automatically switch the active I/O from the
alternate path to the primary path unless you previously instructed it not to by using the
pvchange LVM command.
After initial volume-group setup, path management is manipulated at the physical-volume level
using HP-UX pv... commands. To display the paths to a device, and the status of each path,
use the HP-UX pvdisplay /dev/dsk/... command. To display the paths to all devices
within a volume-group, use the HP-UX vgdisplay -v command. The following example
show partial output from these commands:
# vgdisplay -v
--- Logical volumes --
LV Name /dev/testdg/testvol1
LV Status available/syncd
LV Size (Mbytes) 10000
Current LE 2500
Allocated PE 2500
Used PV 1
Setting Up Multipathing Software on HP-UX 11i v2 33