Swap function for clone units
Clone units provide a very simple way of implementing swap functionality which can, for example, be used when migrating applications or software versions.
Swapping: for a clone session the previous clone unit is used as the original unit of the session; the previous original unit is used as the new clone unit for the session.
EC offers this function directly. In SHC-OSD it is mapped to the /SWAP-CLONE-SESSION command, see section "Swapping the direction of local replication for clone pairs".
This function is not offered directly with QuickOPC; it can be mapped to a sequence of the /STOP-CLONE-SESSION and /START-CLONE-SESSION commands. After a clone session has been canceled, the previous clone unit is used as the original unit of a new session; the previous original unit is used as the new clone unit for the session. Bidirectional replication is implemented for the clone pair in this way.
As a result, the new versions of an application can, for example, be tested on clone units. After a successful test the clone and original units are swapped. The application can continue to run in the new version without interruption. It is not necessary to reload the application on the original units - which would cause an interruption.
Cascaded clone configuration
The cascaded clone function is offered for ETERNUS DX/AF. This enables a clone unit to be used simultaneously as a unit (original) of another QuickOPC or EC replication. This functionality is included in the clone commands. For such a unit the information function /SHOW-CLONE-SESSION automatically displays both clone relationships in two output lines.
Consequently, for example, consistent data can be generated periodically on clone units
and also be provided and updated automatically on another clone unit. The original clone relationship is not canceled when this happens; no complex copy process is required in the storage system.
The following functions are used in SHC-OSD to support cascaded clone:
For cascaded clone volumes, i.e. for volumes which are both original units and clone units, the
/SHOW-STORAGE-DEVICE-CONFIGcommand displays a “B” for “both” in the column for clone usage.The
/SHOW-CLONE-SESSIONcommand displays two lines with the two relationships of the clone pairs for cascaded clone volumes.The cascaded clone functionality is included in all action commands.