DAB and external disk storage systems

The disk storage systems served by BS2000 (e.g. ETERNUS DX) are high availability disk storage systems which fulfill all availability levels defined by the RAID Advisory Board.

These disk storage systems are protected against catastrophic events by local or remote replication functions, see the “SHC-OSD” manual [6 (Related publications)].

Local replication in storage systems

Local replication in storage systems provides the option of creating (additional) copies of the units within a disk storage system which can then be split and processed separately. This allows the original data to be made available to the main application while simultaneous backup and batch evaluations (which normally require that the application be terminated or interrupted) are carried out on the copy.
See the manual “SHC-OSD” [6 (Related publications)] for more information.

When separating this local mirror pair, it must be ensured that the data of a (read/)write cache has been saved to the disk with DAB. This is ensured if the following conditions are met:

• The pubset was correctly exported, thereby producing both file and cache status consistency.

• The DAB cache areas were released before separation in the imported state with the /STOP-DAB-CACHING command.

• When separating in the imported state, you are able to change the existing DAB cache areas from (temporary) write mode to read mode using the /MODIFY-DAB-CACHING command. If only read cache areas are available for the disks, SHC-OSD allows you to separate a local mirror pair. After separation, the cache areas can be reactivated for write caching using the /MODIFY-DAB-CACHING command.

Separating local mirror pairs in the imported state using the option described above avoids the time-consuming build up of cache data that is required when releasing and recreating the cache areas. This means that you can continue working with optimal cache performance immediately.