Operations When All Copy Paths of REC Are Blocked

If all copy paths are blocked due to certain reasons, the following operations take place.

  • When equivalency is maintained in the synchronous transfer mode

    The processes specified in advance with "Split Mode (*1)" are performed. If data equivalency cannot be maintained between the source and destination, the "When the REC asynchronous transfer method is used or data equivalency is lost in the REC synchronous transfer mode" operations (explained next) are executed.

  • When the REC asynchronous transfer method is used or data equivalency is lost in the REC synchronous transfer mode

    When all copy paths between ETERNUS DX storage systems are blocked, transfers are temporarily suspended and the update data is recorded to the copy source during that time. After the cause of the blockage is removed, the copy paths recover automatically. A copy is performed for each session according to "Recovery Mode (*2)" specified in advance. After each session is recovered automatically (Automatic Recovery) or manually (Manual Recovery), the accumulated update data is transferred to the copy destination to restore the equivalent state.

*1 : 

Split mode is a mode that specifies the behavior when all copy paths are disconnected. Select either "Automatic Split" or "Manual Split".

  • Automatic Split

    When a communication error occurs, the REC session is automatically disconnected so that the update process to the copy source can be continued.

  • Manual Split

    When a communication error occurs, the operator decides whether to disconnect the REC session. If the session is disconnected in all the copy paths, operations that include the update process on the server side cannot continue.
*2 : 

Recovery mode is a mode that specifies the recovery method when recovering from REC communication errors. Select either "Automatic Recovery" or "Manual Recovery".

  • Automatic Recovery

    When the communication line that is disconnected due to an error is restored, the REC session is recovered automatically.

  • Manual Recovery

    Even when the communication line that is disconnected due to an error is restored, the REC session is not recovered automatically. It must be recovered manually.
Figure: Copy Operation When All Copy Paths Are Blocked

(1) Equivalent state

(2) All paths are blocked

(3) Update information is accumulated

(4) Accumulated updates are transferred when the path is cleared

(5) Restored to the equivalent state

If a failure occurs and all the paths are blocked under equivalent state, the safety of the data at the destination is guaranteed while all the paths are blocked. However, the safety of this destination data is not guaranteed until the paths are recovered, any pending data updates are transferred, and the source and destination data are made equivalent. When REC is used for disaster recoveries, "Recovery Mode" must be selected after these specifications are taken into consideration. Consult with your maintenance engineer for information on how to recover paths when all paths are blocked.