The software product SHC-OSD (Storage Host Component) offers various clone functionalities. More information can be found in the chapter "Local replication with clones" in the manual „SHC-OSD“ [14]
With SHC-OSD it is possible to create consistent clone units of a pubset during operation. Suspending all I/Os on all affected units of a pubset during the split ensures data consistency across all disks in the pubset. This can then be used, among other things, to create an FDDRL backup of the home pubset without interrupting operations. In addition, the clone units are supplied with the current F5 label, so that FDDRL only has to save the allocated areas of the disk during the backup.
The procedure for creating the clone units differs depending on the replication function:
QuickOPC-Clone on ETERNUS DX/AF
You can find more information on this in the QuickOPC (ETERNUS DX / AF) chapter in the “SHC-OSD” [14].
At certain times, QuickOPC creates clone units from the original units with the commands:
/START-CLONE-SESSION UNIT=*BY-PUBSET(PUBSET=<catid>,NEW-PUBSET=*SAME / *SPECIAL-VSN / <catid>, HOLD-IO=*UNTIL-ACTIVATED, WAIT=*UNTIL-SYNCHRONIZATION
or
/RESTART-CLONE-SESSION UNIT=*BY-PUBSET(PUBSET=<catid>,NEW-PUBSET=*SAME / *SPECIAL-VSN / <catid>, HOLD-IO=*UNTIL-ACTIVATED), WAIT=*UNTIL-SYNCHRONIZATION
Before the clone can be used (by FDDRL), it must be in the SPLIT status.
The parameter WAIT=*UNTIL-SYNCHRONIZATION waits for the end of synchronization and simplifies the processing of procedures if an FDDRL backup is then carried out.
EC-Clone on ETERNUS DX/AF
More information can be found in the chapter "Equivalent Copy (EC, ETERNUS DX / AF)" in the manual "SHC-OSD" [14].
By executing the /START-CLONE-SESSION command, the synchronization of the clone pair is started implicitly. After the initial synchronization has ended, the pair is in the SYNCHRONIZED status.
In this status, the clone units can be separated using the /ACTIVATE-CLONE command:
/ACTIVATE-CLONE UNIT=*BY-PUBSET (PUBSET=<catid>, NEW-PUBSET=*SAME / *SPECIAL-VSN / <catid>, HOLD-IO=*UNTIL-ACTIVATED
After the clone pair has been activated, it enters the SPLIT state.
Parameter NEW-PUBSET=*SAME / *SPECIAL-VSN / <catid>
The NEW-PUBSET parameter of the /START-CLONE-SESSION, /RESTART-CLONE-SESSION and /ACTIVATE-CLONE statements can be used to determine which VSNs are assigned to the cloned disks.
FDDRL backup of clone units with SPECIAL-VSN (NEW-PUBSET=*SPECIAL-VSN)
For an FDDRL backup, it is recommended to use the parameter NEW-PUBSET=*SPECIAL-VSN. This gives the clone units special VSNs. The existence of disks with identical VSNs is avoided.
With the FDDRL statements DUMP-DISK and DUMP-PUBSET and the operand SPECIAL-VSN=*YES, FDDRL requests these disks renamed with special VSNs for processing. The operand SPECIAL-VSN=*YES is used for disk allocation and indicates that these disks are additional disk units specially renamed by SHC-OSD. The disks are backed up as if they had their original VSN. They can be restored under the original VSN.
FDDRL backup of clone units with renaming (NEW-PUBSET=<catid>)
Renaming the pubset with the parameter NEW-PUBSET=<catid> for FDDRL backup is not recommended.
Only SF pubsets can be renamed explicitly; But even there, dealing with renamed pubsets creates additional work when managing the backups and restoring (PVSREN). After the explicit renaming, FDDRL saves the pubset with a new catalog ID. It should be noted that the old catalog ID is used in files of applications (e.g. procedures).
FDDRL backup of clone units without renaming (NEW-PUBSET=*SAME)
A separation without renaming creates disks with an identical VSN. On the one hand, this means that with the FDDRL backup, the mounting request must be answered individually for each disk. On the other hand, even after a crash during the separation, the operator has to distinguish the disks with double VSN during IMPORT-PUBSET processing.
Write caching with DAB must be ended before the disconnection so that all data is written to the disks.
Parameter HOLD-ID
HOLD-IO=*UNTIL-ACTIVATED parameter is important so that all clone units in a pubset have a consistent status.The WAIT=*UNTIL-SYNCHRONIZATION parameter waits for the synchronization to be completed and thus simplifies the processing of procedures if an FDDRL backup is then performed.