CP6100 I/O Process Programming Manual

File System Error Codes
In the following protocols, recovery from a path switch is
somewhat simplified:
• In ADCCP a path switch doesn't change the state of the line.
You can retry your request without loss or duplication of
data.
• In BSC or MPSB you can set the parameter xxxNONSTOPON, where
xxx is the acronym that represents the protocol; then a path
switch won't change the state of the line, and you can retry
requests without loss or duplication of data.
The request ID of a retry must match that of the original
request. This feature keeps the protocol from sending the same
data twice or from delivering the same data twice to the
application.
Of course, the behavior of another station can affect recovery.
For instance, if the remote station notes a delay and resets
the line, its action causes a change in state, requiring end-to-
end recovery. CP6100 fault-tolerance cannot extend beyond the
subsystem cabinet.
TOTAL SUBSYSTEM AND LIU FAILURES
Sometimes an error condition affects more than one path to a
device. CP6100 attempts to recover from such failures in a way
that has the least possible impact on running applications.
If no path exists between the controllers and the 6100 subsystem
cabinet--for instance, if both cables are unplugged or the
subsystem cabinet has no power--CP6100 queues user requests and
completes them every 30 seconds with file system error 231. When
power returns, CP6100 downloads the line. Applications can
resume using the line, with the following considerations:
• If the SYSGEN AUTOCLOSE parameter is set, applications must
close and reopen the line to use it again.
• If the SYSGEN AUTOCONF parameter is set and applications have
made configuration changes, those changes must be restored
(because the configuration block has been overwritten).
• The delay resulting from the failure may have caused a timeout
or loss of the communication link. It may be necessary to
perform end-to-end recovery.
These same considerations apply whenever the line is downloaded,
whether because of a CMI START command or in the course of error
recovery.
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