Managing HP Serviceguard A.11.20.20 for Linux, March 2014

• If you are using a storage device that does not support SPC-3 PR, disable the PR support using
the FORCED_PR_DISABLE flag in the cluster configuration.
• If you are using Serviceguard Manager for creating modular packages, PR module is displayed
as optional. However, HP recommends that you always enable PR module for creating the
modular packages.
• The udev alias names must be created using symlinks. For more information about how to
create udev alias names using symlinks, see the Using udev to Simplify HP Serviceguard for
Linux Configuration white paper at http://www.hp.com/go/linux-serviceguard-docs.
• PR is available in serviceguard-xdc packages. For more information, see HP Serviceguard
Extended Distance Cluster for Linux A.11.20.20 Deployment Guide.
• The LUN device must support PR and be consistent with the SPC-3 specification
• PR is not available in legacy multi-node packages.
PR is available in modular multi-node packages, and in both modular and legacy failover
packages.
◦ All instances of a modular multi-node package must be able to use PR; otherwise it will
be turned off for all instances.
• The package must have access to real devices, not only virtualized ones.
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
in the event of a catastrophic cluster failure. You need to make sure that this script is run in that
case; the LUN devices could become unusable otherwise. See “Revoking Persistent Reservations
after a Catastrophic Failure” (page 255) for more information.
3.7.2 How Persistent Reservations Work
You do not need to do any configuration to enable or activate PR, and in fact you cannot enable
it or disable it, either at the cluster or the package level; Serviceguard makes the decision for each
cluster and package on the basis of the Rules and Limitations described above.
When you run cmapplyconf (1m) to configure a new cluster, or add a new node, Serviceguard
sets the variable cluster_pr_mode to either pr_enabled or pr_disabled.
• ENABLED means that packages can in principle use PR, but in practice will do so only if they
meet the conditions spelled out under “Rules and Limitations”.
• DISABLED means that no packages can use PR
You can see the setting of cluster_pr_mode in the output of cmviewcl -f line; for example:
...
cluster_pr_mode: pr_enabled
NOTE: You cannot change the setting of cluster_pr_mode.
If a package is qualified to use PR, Serviceguard automatically makes and revokes registrations
and reservations for the package's LUNs during package startup, and revokes them during package
shutdown, using the sg_persist command. This command is available, and has a manpage,
on both Red Hat 5, Red Hat 6, and SUSE 11 .
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.)
74 Understanding Serviceguard Software Components