Guidelines for defining GTF trace output data sets in a cataloged procedure

The trace output data sets must be specific to each instance of GTF and can be defined in the cataloged procedure. Each instance of GTF to be started must have a separate cataloged procedure, or if the same cataloged procedure is used, then a different trace data set must be supplied with the START command

Use the following guidelines for specifying trace output data sets on the IEFRDER DD or GTFOUTxx DD statements:

You can define up to 16 output data sets for GTF to use. If you define more than 16 data sets, GTF will accept the first 16 and ignore the rest.
If GTF cannot open all of the data sets, it issues a message that identifies those that are unopened, and continues processing with those that are open.
Do not specify the RLSE option while using the SPACE parameter because the output data sets are opened and closed more than once while GTF runs.
Note: If the GTF trace output resides on a SMS managed volume you should ensure the SMS management class does not allow partial release.
Do not request secondary extents for trace data sets. GTF will only use the first extent.
To obtain the maximum degree of control over the number of trace entries for which space is allocated, specify space allocation in blocks, using a block length that matches the BLKSIZE of your trace data set. Do not specify any secondary space. Use the CONTIG option to request contiguous blocks. For example, if your BLKSIZE is 8192, code the SPACE keyword as follows:
```
SPACE=(8192,(500,0),,CONTIG)
```
All data sets must be in the same device class: either DASD or tape, but not both. If you mix device classes, GTF will ignore the tapes and use only DASD. However, the data sets can have different device types; for example, you can mix 3380 and 3390 device types.
DSNTYPE=LARGE data sets are treated like conventional data sets except they can occupy more than 64K tracks per volume.
VSAM linear data sets are treated like conventional data sets. The use of a data set is rejected if it does not comply to the 32K control interval size requirement. The VSAM extended addressing option is accepted.
When WRAP processing is requested, the primary space request is consulted and only control intervals contained within that space are used. Unlike non-VSAM data sets used for WRAP processing, the primary space does not have to be satisfied using a single extent. A data set must be empty or have been defined with the REUSE attribute. If neither of the two conditions exists, GTF rejects the use of the data set.

When WRAP processing is not requested, control intervals are filled until GTF is stopped or the data set is full.

Note: GTF and CTRACE accept a single VSAM linear data set as output. VSAM's support for striping can increase data rate without the complexity associated with the use of distinct data sets.
GTF and CTRACE support placement of NOWRAP traces in cylinder-managed space. WRAP traces placed in VSAM linear data sets can reside in cylinder-managed space too. WRAP traces in non-VSAM data sets cannot be placed in large format data sets, extended format data sets, or cylinder-managed space.
To ensure the most efficient GTF processing, do not specify any particular block size for the output data set or data sets in either:
- The cataloged procedure for GTF
- The JCL, TSO/E commands, or interactive system productivity facility/program development facility (ISPF/PDF) panels that you might use to preallocate the data set or data sets
The system computes an optimal block size when it opens each data set. EXCEPTION: If you want GTF to use an unlabeled tape as the output data set, you must specify the logical record length and block size when you allocate that data set.
If you define more than one data set, you should ensure that the number of paths to the data sets equals the number of data sets.
You can specify the number of channel programs for each output data set using the NCP parameter on each DD statement. The NCP value determines the rate at which GTF transfers data to the output data sets. For example, if you want to transfer data to your data sets at a rate of 25 buffers per second and you have 5 data sets, you will need to specify an NCP value of 5. GTF then transfers data to the 5 data sets at a rate of 5 buffers per second per data set for a total rate of 25 buffers per second.
The maximum value for NCP is 255. If you do not specify a value for NCP, or if you specify a value less than four, GTF will use the following default values:
- For tape: four
- For DASD: the number of output blocks per track, multiplied by four.
If, when you enter the START command, you override any of the DD statements for multiple output data sets, you must use symbolic parameters in those DD statements. See Using the START command to invoke GTF for more information.