Intel 7xx Servers, 170 Servers, AS/400 RISC Server manual Use of Multiple Backup Devices

15.8 The Use of Multiple Backup Devices

Concurrent Saves and Restores - The ability to save or restore different objects from a single library/directory to multiple backup devices or different libraries/directories to multiple backup devices at the same time from different jobs. The workloads that were used for the testing were Large Database File and User Mix from libraries. For the tests multiple identical libraries were created, a library for each backup device being used.

Parallel Saves and Restores - The ability to save or restore a single object or library/directory across multiple backup devices from the same job. Understand that the function was designed to help those customers, with very large database files which are dominating the backup window. The goal is to provide them with options to help reduce that window. Large objects, using multiple backup devices, using the parallel function, can greatly reduce the time needed for the object operation to complete as compared to a serial operation on the same object.

Concurrent operations to multiple backup devices will probably be the preferred solution for most customers. The customers will have to weigh the benefits of using parallel verses concurrent operations for multiple backup devices in their environment. The following are some thoughts on possible solutions to save and restore situations. Remember that memory, processors and DASD play a large factor in whether or not you will be able to make use of parallel or concurrent operations that can be used to affect the back up window.

-For save and restore with a User Mix or small to medium object workloads, the use of concurrent operations will allow multiple objects to be processed at the same time from different jobs, making better use of the backup devices and the system.

-For systems with a large quantity of data and a few very large database files whether in libraries or directories, a mixture of concurrent and parallel might be helpful. (Example: Save all of the libraries/directories to one backup device, omitting the large files from the library or the directory the file is located in. At the same time run a parallel save of those large files to multiple backup devices.)

-For systems dominated by Large Files the only way to make use of multiple backup devices is by using the parallel function.

-For systems with a few very large files that can be balanced over the backup devices, use concurrent saves.

-For backups where libraries/directories increase or decrease in size significantly throwing concurrent saves out of balance constantly, the customer might benefit from the parallel function as the libraries/directories would tend to be balanced against the backup devices no matter how the libraries change. Again this depends upon the size and number of data objects on the system.

-Customers planning for future growth where they would be adding backup devices over time, might benefit by being able to set up Backup Recovery Media Services (BRMS/400) using *AVAIL for backup devices. Then when a new backup device is added to the system and recognized by BRMS/400 it will be used, leaving the BRMS/400 configuration the same but benefiting from the additional backup device. Also the same is true in reverse: If a backup device is lost, the weekly backup doesn't have to be postponed and the BRMS/400 configuration doesn't need to change, the backup will just use the available backup devices at the time of the save.

IBM i 6.1 Performance Capabilities Reference - January/April 2008
© Copyright IBM Corp. 2008	Chapter 15. Save/Restore Performance	248