Before you start using the API trace facility, you must have at least one pre-allocated, sequential data set to contain the trace data. APPC/MVS limits the number of API trace data sets per z/OS system to fifty. This limit is imposed to control the possible impact on performance; collecting and writing trace data are resource-intensive activities that might affect not only APPC/MVS work, but also other system work. On a test system, performance might not be a major concern; on a production system, you may use API tracing options that further limit tracing activity to an acceptable level, with little or no impact on performance.