Managing HP Serviceguard for Linux Ninth Edition, April 2009

Rules and Limitations
Serviceguard automatically implements PR for packages that use LUN storage, subject
to the following constraints:
• 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.
This means that HPVM guests running as cluster nodes cannot use PR.
NOTE: PR is turned off at the cluster level if any node is an HPVM guest.
• Clusters that have nodes that are VMware guests can use PR, with the following
restrictions:
— Two or more VMware guests acting as nodes in the same cluster cannot run
on the same host.
(A cluster can have multiple VMware guests if each is on a separate host; and
a host can have multiple guests if each is in a different cluster.)
— Packages running on VMware guests must use Raw Device Mapping to access
the underlying physical LUNs.
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 274)
for more information.
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.
86 Understanding Serviceguard Software Components