Replicas are created by copying from the source volume to the replica volume using the EC or REC function of ETERNUS Disk storage system.
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.
swsrpmake (Replication creation command) flushes the file system buffer of the source 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 swsrpstartsync (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 swsrpmake (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 system 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.
