BRMS save commands and control groups can be set up to do backups to multiple tape volumes at the same time by using the Parallel device resources field. Parallel saves are done by BRMS in serial parallel format. Serial parallel format indicates the data for each library is only written to one volume at a time but multiple libraries are written at the same time.
Parallel parallel format indicates the data for each library is written to multiple volumes at the same time. The following command can be run to indicate that BRMS should use parallel parallel format when Parallel device resources are specified for BRMS save command or control group:
CRTDTAARA DTAARA(QTEMP/QSRPARFMT) TYPE(*CHAR) LEN(1)
- A serial save is done instead of a parallel save when the save does not support writing to parallel devices, for example if *ALLUSR, *IBM or *NONSYS is specified for the Library (LIB) parameter on the Save Library (
- In releases IBM i 7.1 and IBM i 6.1, the following PTFs or their superseding PTFs are required:
- In release V5R4M0, parallel saves of *IBM, *ALLUSR, generic libraries or a list of libraries may result in either parallel-parallel or serial-parallel format. To force serial-parallel format for *IBM, *ALLUSR, generic libraries or a list of libraries, run the following command:
CRTDTAARA DTAARA(QUSRBRM/Q1APRLNONE) TYPE(*CHAR) LEN(1)
Performance considerations when saving and restoring data in parallel-parallel format
While it is possible to force a parallel-parallel save of *ALLUSR, performance will not always be better and restoring parallel saved data may take longer.
Saving data in parallel-parallel format generally performs worse on most libraries than other available alternatives. The bottleneck is often the system preprocessing of the data rather than the tape I/O. Saving these libraries in parallel-parallel format would just replicate more descriptive data to tape without doing anything to address the real bottleneck.
Parallel data may be restored from fewer tape drives than the save operation spread the data across. Fully recovering the data requires reusing one or more of these drives multiple times. A restore operation can only maintain one library in a partially restored state after the first use of the drives. Therefore, a restore operation can only restore parallel-parallel format data if a single library is specified. (*ALLUSR generics etc are not supported)