The primary storage used by a DASD-only log stream consists of:
No data is written to coupling facility structures. In its use of staging data sets, a DASD-only log stream is similar to a coupling facility log stream defined with DUPLEX(YES) COND(NO).
When the staging data set reaches its HIGHOFFLOAD limit, data is either deleted or offloaded until the LOWOFFLOAD limit is reached.
The following principles apply to DASD-only log streams as much as to coupling facility log streams:
The basic principles of sizing the staging data set for a DASD-only
log stream are the same as those for sizing a staging data set for a coupling
facility log stream, as described in Tuning the size of staging data sets. You should take
the values that you obtain as a starting point, and monitor your logger environment
to adjust the size of the staging data set.
If you are migrating from CICS/ESA 4.1 or CICS/ESA 3.3, you are strongly recommended to use the DFHLSCU program to size your staging data sets. For information about DFHLSCU, see the CICS® Operations and Utilities Guide.
If for any reason you cannot use DFHLSCU, you can use the following formula to calculate a starting point for the size of the staging data set for the system log. The formula calculates the value to be specified on the STG_SIZE parameter of the logstream definition; that is, the size is expressed as a number of 4K blocks.
The values for the number
of log writes per second and buffer puts per second can be taken from your
CICS statistics. In CICS Transaction Server releases, the Logstream statistics
fields collect these statistics as "write requests" (LGSWRITES) and "buffer
appends" (LGSBUFAPP), and you can divide the totals by the number of seconds
in your statistics interval.
If you want to make a more accurate estimate for the size of the
staging data set, consult the following documents:
You are also recommended to consult the IBM Redpaper which is cited in Logging and journaling: performance considerations.