Plan space for DASD log data sets

You can specify the size for DASD log data sets for each log stream on the LS_SIZE parameter in the log stream definition in the LOGR policy.

When specified, the LS_SIZE value is used for allocation request for log stream data set. The value overrides the space allocation attributes for the data class, which can either be explicitly specified in the LS_DATACLAS parameter, or assigned by the DFSMS Automatic Class Selection (ACS) routines. The actual data set size allocated depends on factors such as track size, CISIZE, volume type, and so on.

The smallest size that a log stream data set can be defined for system logger use is 64 KB. If the data set size is too small, logger automatically attempts to reallocate the size large enough for use.
The largest size that a log stream data set can be defined for logger use is up to 4GB.
If trying to achieve a data set near 4 GB in size, see Testing log data set parameter modifications for important notes on choosing and testing data set size changes.

IBM® recommends that you size the data sets as large as your installation can afford to make them. This will minimize the number of log data sets required to represent a log stream. It will also minimize the number of times that system logger must reallocate and switch to using a new log data set when an old one becomes full. Because allocating and switching to a new log data set incurs overhead, it should be done as little as possible.

Start of change IBM recommends that you size offload data sets no smaller than 1 MB, unless the exploiter specifically recommends a size below this amount. End of change

For logrec log stream and OPERLOG, use your current logrec and SYSLOG output data sets as a guide for log data set size. To calculate the log data set size for logrec, add together the logrec data set sizes for all the systems writing to the logrec log stream. For OPERLOG, add the sizes of the SYSLOG data sets for each system in the sysplex and multiply by at least 2, and then use that value as your log data set size. OPERLOG log data sets will generally be at least two times greater than SYSLOG data sets, but the OPERLOG data set size may need to be altered further based on individual experience.

By default, each log stream is limited to a maximum of 168 log data sets unless you define data set directory extent records in the LOGR couple data set and make it the active primary LOGR couple data set. By defining data set directory extent records, a log stream is no longer limited to 168 log data sets.