Saving libraries to multiple devices for a single save operation

A traditional save to a single device produces one or more tape files on the tape media. A media file is produced for each saved library. When data is saved to multiple devices in a single operation, the data can be saved in parallel format. The data in each media file is spread across each device. Each device may contain pieces of each saved object. When saving multiple libraries to multiple devices in a single operation, the data can also be saved in serial format. The data for each media file is entirely written to one device. Each device contains entire libraries.

You can perform a save operation while using more than one media device simultaneously. If you save a single library, the data that is produced on the save media will have a parallel save format. The data is spread across the media devices. If you use Backup, Recovery and Media Services (BRMS), the save format is also parallel.

If you save multiple libraries to more than one media device, the server saves each library to a single device in serial format. If you use BRMS to save multiple libraries to more than one media device, the format could be a mixture of parallel and serial formats.

The following shows when the server will use a parallel or serial save.

Note:

This table shows the default format. However, you now have the capability to specify the media definition and how the devices will be allocated. End of change

Table 1. Library parallel and serial saves
Save scenario	Using SAVLIB, SAVOBJ command ²	Using BRMS
Save one library to multiple devices	Parallel	Parallel
Save multiple libraries to multiple devices	Serial¹	Could be a mixture of parallel and serial¹
1 You can save these libraries in parallel format by creating data area QTEMP/QSRPARFMT. This capability does not apply if LIB(ALLUSR), LIB(IBM), or LIB(NONSYS) is specified on the SAVLIB command. Note: This function is now available through the Create Media Definition (QSRCRTMD) API. 2 To save to multiple devices using the SAVxxx commands, you must use a media definition (MEDDFN).

Start of change This table shows the correlation between the libraries being saved and some possible results of the media files that are produced. End of change

Table 2. Libraries saved
Data saved	Number of devices	Format	Tape media files produced
Library A	1	Serial	A
Library A	2	Parallel	Device 1: A Device 2: A
Libraries A, B, C, D	1	Serial	A, B, C, D
Libraries A, B, C, D	2	Parallel	Device 1: A, B, C, D Device 2: A, B, C, D
Libraries A, B, C, D	2	Serial	Device 1: A,C Device 2: B, D

Once you create a media definition, a convenient way to save all of your user libraries to multiple devices is to specify SAVLIB LIB(*ALLUSR) DEV(*MEDDFN). If you happen to have a particularly large library that you do not want to save in serial format, you could omit that library and save it individually in parallel format.

Backup Recovery Media Services (BRMS) provides an easy to use interface that allows you to perform parallel save operations without creating a media definition. You specify which tape devices to use in parallel, and BRMS builds and manages the media definition for you.