Managing Serviceguard Eighteenth Edition, September 2010

separate mount points. If possible, the application should not assume a specific mount
point.
To prevent one node from inadvertently accessing disks being used by the application
on another node, HA software uses an exclusive access mechanism to enforce access
by only one node at a time. This exclusive access applies to a volume group as a whole.
Use Multiple Destinations for SNA Applications
SNA is point-to-point link-oriented; that is, the services cannot simply be moved to
another system, since that system has a different point-to-point link which originates
in the mainframe. Therefore, backup links in a node and/or backup links in other nodes
should be configured so that SNA does not become a single point of failure. Note that
only one configuration for an SNA link can be active at a time. Therefore, backup links
that are used for other purposes should be reconfigured for the primary mission-critical
purpose upon failover.
Avoid File Locking
In an NFS environment, applications should avoid using file-locking mechanisms,
where the file to be locked is on an NFS Server. File locking should be avoided in an
application both on local and remote systems. If local file locking is employed and the
system fails, the system acting as the backup system will not have any knowledge of
the locks maintained by the failed system. This may or may not cause problems when
the application restarts.
Remote file locking is the worst of the two situations, since the system doing the locking
may be the system that fails. Then, the lock might never be released, and other parts
of the application will be unable to access that data. In an NFS environment, file locking
can cause long delays in case of NFS client system failure and might even delay the
failover itself.
Using a Relocatable Address as the Source Address for an Application that
is Bound to INADDR_ANY
CAUTION: The procedure in this section depends on setting the HP-UX kernel
parameter ip_strong_es_model. HP supports setting this parameter for use with
Serviceguard only if you are not using a cross-subnet configuration (page 41). Otherwise,
leave the parameter at its default setting (zero, meaning disabled) and do not attempt
to use the procedure that follows.
In an application for which INADDR_ANY is set, the procedure that follows enables
HP-UX to use a relocatable package IP address on the same subnet as the source address
of outgoing IP data packets, instead of automatically selecting the physical network IP
address of the interface.
The procedure uses the HP-UX parameter ip_strong_es_model to enable per-interface
default gateways. These default gateways are created for secondary network interfaces
when you add a relocatable package IP address to the system. When the
Using a Relocatable Address as the Source Address for an Application that is Bound to INADDR_ANY 435