gtpm1m3o | TPF V4R1 Migration Guide: 3.1 to 4.1 |
In the TPF 4.1 system, the Capture and Restore package is enhanced in the way that it distributes simultaneous captures. Rather than trying to calculate channel utilization, you specify the maximum number of captures allowed for each tape control unit and DASD and tape channel path on the new ZFCAP command.
The tape update utility maintains two tables, the channel usage table and the device control unit usage table, which maintain the count of effective captures and restores taking place on the channel path or control unit.
See TPF Database Reference for more information about the Capture and Restore package.
Capture uses the tape devices you specify on the ZFCAP start Capture commands for capturing DASD devices. In the TPF 3.1 system, Capture kept track of which tape device was used last, and continued the Capture on the next device you specified. In the TPF 4.1 system, when Capture needs another tape device, it selects the first available tape device, regardless of which tape device it just used. This affects your operational procedures for running Capture on both single and multiple DASD modules.
In the TPF 4.1 system, when you are running Capture on a single DASD module that requires more than one tape, only two tape devices are used, regardless of how many devices you specify on the ZFCAP command. Capture will use the first device you specify, then the second device, then the first device again.
For example, in the TPF 3.1 system, if you wanted to start Capture on DASD module 047, and you wanted to use tape devices 580, 581 and 582, you would enter ZFCAP MOD 047 580/581/582.
Capture would have selected each of the three tape devices in the order in which they display in the message. In the TPF 4.1 system, however, Capture selects device 580, then 581, then switches back to 580. Device 582 does not participate in the Capture operation. Only two tape devices are used. To specify that the two devices you want to use are 580 and 581, the correct way to specify the device pair is by entering ZFCAP MOD 047 580-581.
In the TPF 4.1 system, there is no way to associate more than two tape devices with one DASD module.
When you run Capture on multiple modules, Capture again searches for the first available tape device. This has two different effects depending on whether your DASD modules can be captured on one tape or require multiple tapes.
If your DASD module capture fits on one tape, the tapes will be selected in the order you specify based on availability. For example, if you wanted to start Capture on all your modules on a list of tape devices in the TPF 3.1 system, you would have entered ZFCAP ALL 580/581/582/....
The first module would be captured on device 580, the next module on device 581, and so on. But in the TPF 4.1 system, depending on your tape configuration and procedures, Capture will use device 580, then 581, then; if 580 is available, it will use 580 next.
If your capture requires more than one tape per module, you can specify tape devices in pairs to ensure that each module is captured on the same two devices by entering ZFCAP ALL 580-581/582-583/584-585/.... This way a pair of tape devices will be used to capture each module.
You need to integrate these changes with the new load balancing support to ensure that Capture runs with minimal impact to the system and that tape devices are selected properly.
The DASDCU, DASDCH, TAPECU, and TAPECH parameters are provided to balance the resource loads required by Capture. You can set all of these parameters, except DASDCU. See TPF Operations for more information about these parameters.
The techniques used for balancing capture loads require a configuration change for some IBM 3990 models:
The limited lock facility (LLF) static switch may cause even and odd addresses to be placed on different channels (for example, 4E0, 6E1, 4E2, 6E3, and so on). However, for proper operation of load balancing, all the device addresses of these control units must have the same channel address. This is not a concern for the IBM 3990 Model 3 running record cache.
Load balancing is directly related to site resource requirements and the degree of multipathing found within the configuration. The configuration is described during Input/Output Configuration Program (IOCP) Generation.