Managing HP Serviceguard A.11.20.00 for Linux, June 2012

Unlike exclusive activation for volume groups, which does not prevent unauthorized access to the
underlying LUNs, PR controls access at the LUN level. Registration and reservation information is
stored on the device and enforced by its firmware; this information persists across device resets
and system reboots.
NOTE: Persistent Reservations coexist with, and are independent of, activation protection of
volume groups. You should continue to configure activation protection as instructed under Enabling
Volume Group Activation Protection. Subject to the Rules and Limitations spelled out below, Persistent
Reservations will be applied to the cluster's LUNs, whether or not the LUNs are configured into
volume groups.
Advantages of PR are:
• Consistent behavior.
Whereas different volume managers may implement exclusive activation differently (or not at
all) PR is implemented at the device level and does not depend on volume-manager support
for exclusive activation.
• Packages can control access to LUN devices independently of a volume manager.
Serviceguard's support for the ASM manager allows packages whose applications use these
protocols to access storage devices directly, without using a volume manager.
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.
• 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.
For more information on using Serviceguard with VMware Virtual Machines, see the white paper
Using Serviceguard for Linux with VMware Virtual Machines at http://www.hp.com/go/
linux-serviceguard-docs.
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 227) for more information.
About Persistent Reservations 65