Failure as a result of failback to the local storage system

When the local storage system or the local system is operational again, processing can once more be switched back to the local storage system and the local system. To permit this, the modified data of the remote storage system is transferred to the local storage system. The applications on the standby system are terminated and restarted on the local system. If the home pubset is also affected, the standby system must be shut down.

In symmetrical configurations (known as X configurations) failure as a result of failback can be prevented or deferred to a more suitable time using the SWAP-REMOTE-COPY function. Without interrupting the application, this function enables source units to be changed into target units and target units on which the applications run to be changed into source units. From this point onwards, secure operation with remote copy data replication is ensured, even without failback.

Actions on the local system (Part 1)

1. Prepare the local storage system:

   • Disable all the channels and remote links (to prevent access).

   • Reconnect all the channel or remote link cables.

   • Start the local storage system.

   • Service should check the local storage system for damage.

2. Activate the remove links on the local storage system.

Actions on the standby system

1. Terminate the applications and export the pubsets.

2. Resynchronize the REC pairs (relicts) from the remote storage system to the local storage system with the /RESUME-REMOTE-COPY RESTORE=*TO-SOURCE command.

   If the local storage system contains only source units which are affected by the failure, the entire remote storage system can be specified.

   /RESUME-REMOTE-COPY
     UNIT=*BY-STORAGE(SERIAL-NUMBER=<local serialnumber>
     ,LOGICAL-VOLUMES=*ALL-SOURCE-UNITS),WAIT=*UNTIL-SYNCH,RESTORE=*TO-SOURCE
   

3. Use /DETACH-DEVICE to detach the target units (see the “Commands” manual [1])

For these functions, for SYSTEM-ADMIN-SCOPE or TASK-ADMIN-SCOPE you may have to set the values DETACHED-DEVICES=*ACCEPT and NOT-DEFINED-DEVICES=*ACCEPT (see the /MODIFY-SHC-PROCESSING command, "MODIFY-SHC-PROCESSING Changes settings of SHC-OSD").

Actions on the local system (Part 2)

1. Activate the server channels on the local storage system. The server channels can be set to online once synchronization has been completed.

2. Start the local system.

3. Attach the source units on the local system and resume processing: /ATTACH-DEVICE (see the “Commands” manual [1]).

4. Import the pubsets and start the applications.