Managing HP Serviceguard for Linux Ninth Edition, April 2009

• 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 because at least one node is an
HPVM guest.
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 and SUSE SLES 10.
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 initiators on each node running the package register with LUN devices using the
same PR Key, known as the node_pr_key. Each node in the cluster has a unique
node_pr_key, which you can see in the output of cmviewcl -f line; for example:
...
node:bla2|node_pr_key=10001
When a failover package starts up, any existing PR keys and reservations are cleared
from the underlying LUN devices first; then the node_pr_key of the node that the package
is starting on is registered with each LUN.
In the case of a multi-node package, the PR reservation is made for the underlying
LUNs by the first instance of the package, and the appropriate node_pr_key is registered
each time the package starts on a new node. If a node fails, the instances of the package
running on other nodes will remove the registrations of the failed node.
You can use cmgetpkgenv (1m) to see whether PR is enabled for a given package;
for example:
cmgetpkgenv pkg1
...
PKG_PR_MODE="pr_enabled"
About Persistent Reservations 87