By using the TNSTAT start option or the MODIFY TNSTAT command, you can collect data that will help you set the proper values on resource definition operands that control VTAM® I/O operations in your system.

System management facility (SMF) is required to record tuning statistics. Tuning statistics can optionally be displayed at the system console using the CNSL operand, and statistics are always recorded in the appropriate tuning statistics file. This file is an SMF data set. The tuning statistics record is SMF record type 50. The format depends upon the resource for which the tuning I/O operation is collected. The tables in this section show the formats that can be present in a tuning statistics record.

TNSTAT need not be specified in the VTAM start list to later activate tuning statistics.

No tuning statistics are provided for LANs connected through XCA lines.

Tuning statistics can be activated or deactivated for all devices simultaneously (global tuning statistics), and tuning statistics can also be activated or deactivated based on a TRLE name (TRLE tuning statistics). When a TRLE is first activated, the tuning statistics state for that TRLE is set to the global tuning statistics state. For instance, if global tuning statistics are active, TRLE tuning statistics are active for that TRLE.