Starting or restarting an XRC session

Use the XSTART command to start an XRC session or to restart a suspended session.

You can start an XRC session automatically at system initialization time by putting the JCL for a TSO job, that includes the XSTART command, in a SYS1.PROCLIB member.
The operating system then starts the SYS1.PROCLIB member from a SYS1.PARMLIB COMMANDxx member.

Note: The storage administrator must issue the XSTART command to start an XRC session if the SYS1.PROCLIB member does not include the XSTART command.

XRC can either be restarted or experience a new start, depending on the steps taken after issuing an XSUSPEND command. XRC will undergo a new start if an XRECOVER command is issued following the XSUSPEND command. If a XRECOVER command is not issued, XRC can restart. A new start will always occur after you issue an XEND command to end the session; however, a restart is not possible at that point.

When an error occurs and you have specified ERRORLEVEL(SESSION), XRC suspends all volumes in the session but leaves the XRC session active. XRC leaves the secondary volumes in a consistent state within the suspended session. You can correct the error and add the volumes to the active session without having to restart the session. There is minimal impact to the primary application. XRC can rapidly resynchronize the suspended volumes when you add them to the session. This is possible because either hardware bitmaps or software bitmaps maintain the changes to data on the primary volumes.

The following command starts the XRC session with error level set to SESSION. All of the volumes in the session contain associated data. If an error to a volume in duplex status occurs, XRC suspends all volumes in the session. If an error occurs with a coupled, interlocked session, the volumes in all coupled sessions are suspended.

 XSTART DALLAS SESSIONTYPE(XRC) ERRORLEVEL(SESSION)

In the preceding example, the minimum syntax supported is:

 XSTART DALLAS S(XRC) E(SESSION)

The following command starts an XRC session with the error level set to VOLUME. XRC suspends any active volume pair that encounters an error.

  XSTART DALLAS SESSIONTYPE(XRC) ERRORLEVEL(VOLUME)

Note: When you restart a suspended XRC session with the XSTART command, the system data mover determines which tracks require resynchronization on all of the suspended volumes. The resynchronization process does not occur, however, until you issue an XADDPAIR command for the volume pair.

For additional information about the XSTART command, refer to XSTART–Starting a session.