Replicas are created by copying from the source volume to the replica volume using the EC or REC function of ETERNUS disk storage systems.
Synchronized replication uses two methods to create a copy: full copying and incremental copying. In the case of full copying, all of the source volume is completely copied. In the case of incremental copying, only the data that has been updated since the last replication is copied.
Creating replicas with full copying
Use this method to create the first copy in a replication.
Creating copies with incremental copying
Use this method to create copies in the future once a previous replica exists.
Copies are created by reflecting the data that has been updated after an initial copy has been made (full copying and incremental copying).
The procedure for synchronized replication incorporates the following steps:
Full copying starts when synchronized processing that has been invoked using swsrpstartsync (Synchronous processing start command) starts copying from the source volume to the replica volume. Refer to step (1) in the figure below
Full copying is completed when the source volume and replica volume both attain the equivalency maintenance status. From this point on, updates in the source volume are subsequently reflected in the replica volume, so that data equivalence is always maintained (this is called an equivalency maintenance state). Refer to the states in steps (2) and (3) in the figure below
Synchronized processing is temporarily stopped with swsrpmake (Replication creation command) to create a copy of the source volume.
The replication creation command dismounts or mounts the original volume.
This processing determines the scope of original data (for details of this, refer to "Appendix C Pre-processing and Post-processing of Replication". After execution of the replication creation command, the replica volume can be accessed (copy established status). Refer to the states in steps (3) and (4) in the figure below
To create another copy, the synchronized processing that has been temporarily stopped is restarted with the synchronous processing start command. In the case of this copy, the only data copied to the replica volume is the data on the source volume that has been updated since the previous copy was made. Refer to step (4) in the figure below.
When the replica volume has been updated after the previous copy is made, the contents of the update of the replica volume are cleared.
When the incremental data has been copied, the status returns to the equivalency maintenance state. Refer to the states in steps (5) and (6) in the figure below.
When this status has been set, the copy is re-created with the replication creation command. Refer to step (6) in the figure below.
Figure 7.9 Synchronized replication processing
Note
When using the EC or REC function in synchronized replication, ETERNUS disk storage systems must support the EC or REC function.
swsrpmake (Replication creation command) cannot be executed unless both the source volume and replica volume are in an equivalent state.
Note
If the backup volume is part of a volume group, do not execute the vgchange (1M) command under synchronous processing (EC/REC) execution. If the backup volume becomes deactivated during the execution of synchronous processing, it is not only impossible to make it active again but it will be in a state such that operations including stopping synchronous processing, the backup execution command, and the backup synchronous processing cancel command, cannot be performed.
When you have accidentally deactivated the backup volume, reactivate it after performing a forced stop of the synchronous processing using GRmgr etc.
