Sizing the staging data sets for DASD-only log streams

To size data sets for a DASD-only log stream, you can either take the system logger defined default size or define your own size on the STG_SIZE parameter in the log stream definition in the LOGR policy. The default minimum size is 64KB, and the recommended minimum is 10MB.

IBM® recommends that staging data sets be sized no smaller than 10 MB, unless the exploiter specifically recommends a size below this amount. The IBM recommended minimum is intended to assist in avoiding staging data set full conditions. These conditions may lead to poor application performance or possibly exploiter outages.

Note: The staging data set should be sized large enough to allow normal offload activity to keep up with the pace at which IXGWRITE requests are received.

To determine the default staging data set size for a DASD-only log stream, system logger does one of the following, in the order listed:

Uses the STG_SIZE of the log stream specified on the LIKE parameter, if specified.
Uses the size defined in the SMS data class for the staging data sets.
Uses dynamic allocation rules for allocating data sets, if SMS is not available.

Note that if both the STG_DATACLAS and STG_SIZE parameters are specified for a log stream, the value for STG_SIZE overrides the STG_DATACLAS value.

The resulting staging data set size can be up to 4GB. For important notes on choosing and testing log data set size changes, see Testing log data set parameter modifications.