OpenVMS Cluster Systems - OpenVMS Systems - HP

Building Large OpenVMS Cluster Systems
9.7 Adjusting System Parameters
5. Check to see whether the number of CR_WAITS (credit waits) logged
against the VMS$VAXcluster connection for any remote node is incrementing
regularly. Ideally, credit waits should not occur. However, occasional waits
under very heavy load conditions are acceptable.
How to resolve incrementing credit waits:
If the number of CR_WAITS is incrementing more than once per minute, perform
the following steps:
1. Increase the CLUSTER_CREDITS parameter on the node against which they
are being logged by five. The parameter should be modified on the remote
node, not on the node which is running SHOW CLUSTER.
2. Reboot the node.
Note that it is not necessary for the CLUSTER_CREDITS parameter to be the
same on every node.
9.8 Minimize Network Instability
Network instability also affects OpenVMS Cluster operations. Table 9–9 lists
techniques to minimize typical network problems.
Table 9–9 Techniques to Minimize Network Problems
Technique Recommendation
Adjust the
RECNXINTERVAL
parameter.
The RECNXINTERVAL system parameter specifies the number of seconds
the OpenVMS Cluster system waits when it loses contact with a node,
before removing the node from the configuration. Many large OpenVMS
Cluster configurations operate with the RECNXINTERVAL parameter set
to 40 seconds (the default value is 20 seconds).
Raising the value of RECNXINTERVAL can result in longer perceived
application pauses, especially when the node leaves the OpenVMS Cluster
system abnormally. The pause is caused by the connection manager
waiting for the number of seconds specified by RECNXINTERVAL.
Protect the network. Treat the LAN as if it was a part of the OpenVMS Cluster system. For
example, do not allow an environment in which a random user can
disconnect a ThinWire segment to attach a new PC while 20 satellites
hang.
Choose your hardware
and configuration
carefully.
Use the
LAVC$FAILURE_
ANALYSIS facility.
Certain hardware is not suitable for use in a large OpenVMS Cluster
system.
• Some network components can appear to work well with light loads,
but are unable to operate properly under high traffic conditions.
Improper operation can result in lost or corrupted packets that will
require packet retransmissions. This reduces performance and can
affect the stability of the OpenVMS Cluster configuration.
• Beware of bridges that cannot filter and forward at full line rates and
repeaters that do not handle congested conditions well.
• Refer to Guidelines for OpenVMS Cluster Configurations to determine
appropriate OpenVMS Cluster configurations and capabilities.
See Section D.5 for assistance in the isolation of network faults.
Building Large OpenVMS Cluster Systems 9–19