Introduction › How the Started Task Works › Remote Mirroring

Remote Mirroring

The currently available DASD subsystems have the ability to create a real-time, remote mirror image of data. Both the CA Deliver database and checkpoint are candidates for mirroring.

If the CA Deliver checkpoint is mirrored, it is possible to see both RMOCPP05 and RMOCPP06 messages issued. The RMOCPP05 messages can be caused by long busy conditions caused by the hardware. These messages will stop when the long busy condition is dropped by the hardware.

Some additional information is listed below.

• The microcode that creates remote copies can elongate an I/O and produce what is called a 'long busy' condition.

  We have seen 'long busy' conditions that last longer than 30 seconds. We have also seen DASD error recovery re-drive I/O after a 'long busy'.

• The 'long busy' conditions that are presented by the hardware can cause CA Deliver to issue RMOCCP05 messages.

  When a channel program is started for the checkpoint, a timer is also started. If that timer expires without the I/O completing, the RMOCPP05 message is issued.

  The RMOCPP05 messages stop when the 'long busy' ends.

• When a I/O is started, the signaling of its completion is normally accomplished with a single interrupt that gives both Channel End (CE) and Device End (DE) status.

  We have observed that devices that are mirrored remotely many times are providing two I/O interrupts. The first is Channel End (CE) and the second is Device End (DE). This indicates that there can be longer I/O times as well as additional processor time that might be required to process the additional I/O.