OpenVMS Cluster Systems - OpenVMS Systems - HP

Cluster Troubleshooting
C.10 Diagnosing Port Failures
C–22 Cluster Troubleshooting
Configuration 1: The information illustrated in Figure C–2 is represented more
simply in Example C–1. It shows the cables positioned as in Figure C–2, but it
does not show the star coupler or the computers. The labels LOC (local) and REM
(remote) indicate the pairs of transmitting ( T ) and receiving ( R ) cables on the
local and remote computers, respectively.
Example C–1 Crossed Cables: Configuration 1
T x = R
R = = T
LOC REM
The pair of crossed cables causes loopback datagrams to fail on the local computer
but to succeed on the remote computer. Crossed pairs of transmitting cables and
crossed pairs of receiving cables cause the same behavior.
Note that only an odd number of crossed cable pairs causes these problems. If
an even number of cable pairs is crossed, communications succeed. An error log
entry is made in some cases, however, and the contents of the entry depends on
which pairs of cables are crossed.
Configuration 2: Example C–2 shows two-computer clusters with the
combinations of two crossed cable pairs. These crossed pairs cause the following
entry to be made in the error log of the computer that has the cables crossed:
DATA CABLE(S) CHANGE OF STATE
CABLES HAVE GONE FROM UNCROSSED TO CROSSED
Loopback datagrams succeed on both computers, and communications are
possible.
Example C–2 Crossed Cables: Configuration 2
T x = R T = x R
R x = T R = x T
LOC REM LOC REM
Configuration 3: Example C–3 shows the possible combinations of two pairs of
crossed cables that cause loopback datagrams to fail on both computers in the
cluster. Communications can still take place between the computers. An entry
stating that cables are crossed is made in the error log of each computer.
Example C–3 Crossed Cables: Configuration 3
T x = R T = x R
R = x T R x = T
LOC REM LOC REM