In this example, suppose you have only one tape device available, TAP01, available for backup operations. You can use a tape library, such as a 3570, 358x or 3590 device. For the purposes of this example, however, you are using the device as a stand-alone. You must decide how to save two packaged business applications (one for payroll, the other for inventory), a few company-designed programs, and several user libraries.
In this situation, you could use either of the following strategies to back up your data:
Utilizing an *ALLUSR strategy saves all user libraries, but it does not allow specialized recoveries. An *ALLUSR save may also require that you rebuild access paths when restoring the libraries.
Splitting your application and user data into multiple control groups provides the following benefits:
By splitting user libraries and business applications into separate control groups, you can prioritize the order in which BRMS restores your libraries and applications. In addition, a single control group has only one media policy, and one schedule for all the libraries and applications it contains. Multiple control groups, on the other hand, allow you to run different control groups on different days. And, because they use more than one media policy, multiple control groups allow for more flexible retention periods.
To avoid lengthy rebuilds, design your backups so that you do not include database networks in an *ALLUSR or a generic* backup. Separate control groups can save the based-on physical files before their dependent logical files. This way, BRMS can restore the objects in the correct sequence, thereby avoiding lengthy access path rebuilds. However, you need to make sure that you save the physical and logical files with the same underlying system save command. If you save the logical and physical files with different save commands, BRMS cannot save the access paths, even if you specify ACCPTH(*YES).
You can also consider a compromise between these two strategies, especially if you have smaller systems with fewer libraries. Under these circumstances, you can use a combination of *ALLUSR and your own control groups. Use one or more control groups for specific libraries, and another control group containing the *ALLUSR libraries. If you choose this strategy, you need to omit the libraries in your own control groups. This way, you can restore the items in your control groups selectively, on an as-needed basis. You can save less critical libraries on a less frequent basis.
If you save multiple control groups to single device, BRMS processes them serially, one after another. Figure 8 illustrates how you can design a number of control groups to run in sequence.
The manufacturing application (MANUFACT) consists of libraries MANUFLIB1 through MANUFLIB5, and DISTLIB1 through DISTLIB3. These libraries now exist in three separate control groups. You can find the logical files in library MD_LOGICAL. The logical files were built over physical files in libraries MANUFLIB3 and DISTLIB2. To avoid rebuilding the access paths for these logical files after restore, MANUFLIB3 and DISTLIB2 were omitted from the MANUFACT and DISTRIBUTION control groups. Instead, they were included with library MD_LOGICAL in a separate control group called DBNETWORK. The ADHOC control group contains a few user libraries and a few of the smaller applications. The FINANCE and PAYROLL control groups contain the more critical payroll and finance data.
When you process multiple control groups serially, keep the following considerations in mind: