Managing HP Serviceguard A.11.20.20 for Linux, May 2013

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.
3.7.1 Rules and Limitations
Serviceguard automatically implements PR for packages that use LUN storage, subject to the
following constraints:
• PR is supported with Device Mapper (DM) multipath in the modular package. You can use PR
with the following restrictions:
◦ During package startup, Serviceguard performs registration only on active paths. If the
path becomes active after package startup, it remains unusable until the package is
restarted.
◦ Legacy packages do not support PR with multipath.
◦ Persistent Reservation (PR) module pr_cntl internally uses the dmsetup info command
to probe /dev/dm-n devices. In SUSE Linux Enterprise Server 11 SP1, the dmsetup
info command does not support probing /dev/dm-n devices. Therefore, the features
that use /dev/dm-n, such as udev alias cannot be supported with PR. If you are using
udev aliases in serviceguard-xdc environment, then PR module cannot be supported with
that configuration.
NOTE: This restriction is applicable only on SUSE Linux Enterprise Server 11 SP1.
◦ If you are not using the udev alias names, multipath physical volumes names must be in
the /dev/mapper/XXXX or /dev/mpath/XXXX format.
◦ The udev alias names must not be configured in the /dev/mapper/ or/dev/mpath/
directory.
◦ Multipath device alias names must not contain “pN” or “_partN” strings, where N is the
number.
For example, /dev/mapper/evadskp1 or /dev/mapper/evadsk_part1
• If you accidently run the pr_cleanup command on LUNs belonging to a package that is
already running, PR protection is disabled. To enable PR protection, you must restart the
package.
3.7 About Persistent Reservations 73