DSM/Tape Catalog Management Programming Manual

Communicating With MEDIASRV
DSM/Tape Catalog Management Programming Manual—520481-003
2-9
Sending Commands and Retrieving Responses
Sending Commands and Retrieving
Responses
Management applications prepare SPI buffers by using the standard SPI procedures.
After opening a MEDIASRV process for SPI-formatted messages, the applications use
the WRITEREAD procedure to send the command buffers and retrieve the
corresponding responses. For a description of this process, see the Distributed
Systems Management (DSM) Manual.
Stopping a MEDIASRV Process
A MEDIASRV process can stop itself. How and when it does this depends on the value
of the AUTOSTOP MEDIASRV process execution parameter specified when the
MEDIASRV process is started. See the description of this parameter in Starting a
MEDIASRV Process Using the RUN Command on page 2-2.
A MEDIASRV process can also be stopped by a STOP command from a command
interpreter such as TACL, a PROCESS_STOP_ procedure call, or a STOP or ABORT
SPI command from a management process.
Abnormal Process Termination
In the case of any of these failures, part or all of a pending command might be
executed. After starting another MEDIASRV process, you or your application should
check the status of objects that might have been affected by the command. Associated
error and event messages can help you determine the cause of the problem.
•
If a non-fault-tolerant MEDIASRV fails while it is processing a command, the
WRITEREAD call issued by a requesting application returns file-system error 201.
•
If an application opens a fault-tolerant MEDIASRV with sync-depth equal to 0,
and if the primary process is stopped or its CPU fails, the application’s
WRITEREAD procedure call returns file-system error 201.
•
If an application opens a fault-tolerant MEDIASRV process with sync-depth
equal to 1, and if the primary process is stopped or its CPU fails, the backup
process takes over, and the command message is reprocessed. Reprocessing the
command can result in errors because part or all of the command might have been
executed before the backup takeover.
•
If a management application starts a MEDIASRV process that subsequently stops
abnormally, the operating system sends system message –101 to the application.
For more information, see the descriptions of the FILE_OPEN_ procedure
discussion in the Guardian Procedure Calls Reference Manual. For file-system
error descriptions, see the Operator Messages Manual.