COPY-MODE (processing mode)

Remote copying is available in synchronous or in one of the asynchronous processing modes. The initial settings are made when the remote copy pair is created with /START-REMOTE-COPY. The processing mode can be changed using the COPY-MODE operand of /MODIFY-REMOTE-COPY-PARAMETER. The modification can only be made when remote replication is suspended (IN-HOLD status).

• SYNCHronous processing mode
  Processing mode = synchronous processing. All writes are written from the local system to the cache of the local storage system and are forwarded from there to the cache of the remote storage system. The local system is notified on successful completion. Only then the next write can be performed.

  With this processing mode, data is written on the source unit and the target unit after every successful write.
  Synchronous processing mode is the most secure mode.

• ASYNCHronous processing mode
  Processing mode = asynchronous processing with guaranteed data consistency in the event of hardware failure. This mode requires suitably dimensioned remote copy buffers (cache) on the ETERNUS DX/AF storage systems involved.

  In the remote copy status ACTIVE, pairs are also displayed as synchronized when COPY-MODE=ASYNCH.

  In this processing mode there may be more than one pending write. The data on the target units is however always in a state that is consistent across volumes even in the event of failures because the writes are transmitted in bundled form and in the correct order.

• Processing mode ASYNC-STACK
  Processing mode = asynchronous processing without guaranteed data consistency in the event of hardware failure. This mode requires suitably dimensioned REC buffers (cache) on the ETERNUS DX/AF storage systems involved. In this processing mode there may be more than one pending write.

• Processing mode ASYNC-THROUGH
  Processing mode = asynchronous processing without guaranteed data consistency in the event of hardware failure. In this processing mode each input/output is transferred to the remote system with a delay. Through mode cannot be set. It occurs temporarily in the event of internal state changes between modes in the ETERNUS DX/AF storage system.