Managing Serviceguard A.11.20, March 2013

Rules and Limitations
Serviceguard automatically implements PR for packages using volume groups configured on a LUN
storage, subject to the following guidelines:
• The LUN device must support PR and be consistent with the SPC-3 specification.
• PR is enabled for packages with iSCSI disks, but disabled for packages with non-iSCSI disks.
• Packages with a mix of iSCSI and non-iSCSI disks are not supported.
• iSCSI is only supported with modular packages. It is not supported with legacy packages and
the system multi-node package, which is reserved for use for supporting the Cluster Volume
Manager.
• iSCSI storage devices with PR are supported on only LVM volume groups, and not VxVM or
CVM volume groups.
• iSCSI storage devices do not support the configuration of a lock LUN and a lock disk.
CAUTION: Serviceguard makes and revokes registrations and reservations during normal package
startup and shutdown, or package failover. Serviceguard also provides a script to clear reservations.
When nodes or packages are unable to clear the persistent reservation and registration keys on
the LUN, you must run the script that is provided; otherwise, the LUN devices can become
inaccessible while activating the volume group. For more information, see “Revoking Persistent
Reservations after a Failure” (page 333).
NOTE: When adding a new iSCSI volume group to a cluster or when creating a new cluster
with iSCSI volume groups, ensure the volume groups do not have any SCSI-3 persistent reservations.
If they exist, use the pr_cleanup command to clear the reservations. For more information on
the command, see the pr_cleanup(1m) man page.
How Persistent Reservations Work
Persistent Reservation is performed from a Serviceguard node using the port of an open source
utility called sg3_utils. This utility is included in the March 2012 OE Update Release and later.
It is also supported on HP-UX 11i v3 September 2011 (available via web). For information about
sg3_utils, see SCSI Persistent Reservation Utilities Release Notes at http://www.hp.com/go/
hpux-core-docs-11iv3.
To enable the PR feature, the pr_cntl module (page 236) must be included in all the packages
using this feature. See “cmmakepkg Examples” (page 258).
NOTE: The sg/pr_cntl module is added by default in all the new packages that you create.
Serviceguard makes a PR of type Write Exclusive Registrants Only (WERO) on the package's LUN
devices. This gives read access to any initiator regardless of whether the initiator is registered or
not, but grants write access only to those initiators who are registered. (WERO is defined in the
SPC-3 standard.)
All the initiators on every node running the package register with the LUN devices using the same
PR key, known as the node_pr_key. For information about this parameter, see the cmviewcl(5)
man page. Each node in the cluster has a unique node_pr_key, which is displayed in the output
of cmviewcl -f line; for example,
...
node:omni1|node_pr_key=b3640001
Configuration changes are not required to enable or activate PR both at the cluster level or the
package level. Serviceguard makes the decision for each cluster and package on the basis of the
“Rules and Limitations”.
90 Understanding Serviceguard Software Components