Technical data

System Management Features
4.9 OpenVMS Cluster Systems
4.9.5.1 SCA Control Program
The SCA Control Program (SCACP) utility is designed to monitor and manage
cluster communications. (SCA is the abbreviation of Systems Communications
Architecture, which defines the communications mechanisms that enable nodes in
an OpenVMS Cluster system to communicate.)
In OpenVMS Version 7.3, you can use SCACP to manage SCA use of LAN paths.
In the future, SCACP might be used to monitor and manage SCA communications
over other OpenVMS Cluster interconnects.
This utility is described in more detail in a new chapter in the OpenVMS System
Management Utilities Reference Manual: M–Z.
4.9.5.2 New Error Message About Packet Loss
Prior to OpenVMS Version 7.3, an SCS virtual circuit closure was the first
indication that a LAN path had become unusable. In OpenVMS Version 7.3,
whenever the last usable LAN path is losing packets at an excessive rate,
PEDRIVER displays the following console message:
%PEA0, Excessive packet losses on LAN Path from local-device-name -
_todevice-name on REMOTE NODE node-name
This message is displayed after PEDRIVER performs an excessively high rate
of packet retransmissions on the LAN path consisting of the local device, the
intervening network, and the device on the remote node. The message indicates
that the LAN path has degraded and is approaching, or has reached, the point
where reliable communications with the remote node are no longer possible. It is
likely that the virtual circuit to the remote node will close if the losses continue.
Furthermore, continued operation with high LAN packet losses can result in a
significant loss in performance because of the communication delays resulting
from the packet loss detection timeouts and packet retransmission.
The corrective steps to take are:
1. Check the local and remote LAN device error counts to see if a problem exists
on the devices. Issue the following commands on each node:
$ SHOW DEVICE local-device-name
$ MC SCACP
SCACP> SHOW LAN device-name
$ MC LANCP
LANCP> SHOW DEVICE device-name/COUNT
2. If device error counts on the local devices are within normal bounds, contact
your network administrators to request that they diagnose the LAN path
between the devices.
If necessary, contact your COMPAQ support representative for assistance in
diagnosing your LAN path problems.
For additional PEDRIVER troubleshooting information, see Appendix F of the
OpenVMS Cluster Systems manual.
4.9.6 Warranted and Migration Support
Compaq provides two levels of support, warranted and migration, for mixed-
version and mixed-architecture OpenVMS Cluster systems.
Warranted support means that Compaq has fully qualified the two versions
coexisting in an OpenVMS Cluster and will answer all problems identified by
customers using these configurations.
System Management Features 4–11