System Setup › Saving the Logger Data › Defining the Log Stream

Defining the Log Stream

The External Logger requires the creation of a System Logger Log Stream. IBM's Administrative Data Utility program IXCMIAPU is used for this purpose.

See the IBM manual MVS Setting Up a Sysplex for all the options available for this utility.

The following sample JCL is provided in HLQ.CCUUJCL(IXCMIAPU):

//DEFINE   EXEC PGM=IXCMIAPU                                  
//SYSPRINT DD   SYSOUT=*                                      
//SYSIN    DD   *                                             
 DATA TYPE (LOGR)                                             
    DELETE LOGSTREAM NAME(VTAPE.sysid.LOG)                          
    DEFINE LOGSTREAM NAME(VTAPE.sysid.LOG) DASDONLY(YES) RETPD(4)   
           STG_SIZE(12288) LS_SIZE(36864) HLQ(VTAPE) AUTODELETE(YES)

In the sample JCL, the Log Stream name is VTAPE.sysid.LOG where sysid is the system name for the LPAR on which the logging is occurring. This name must be entered as the value of the LogStream attribute in the CA Vtape Parmlib Dynamic Options Section.

If you are defining multiple CA Vtape Complexes on the same LPARs, then changing the Log Stream name to VTAPE.sysid.subsystemid.LOG where subsystemid is the CA Vtape subsystem ID (SVTn where n = 1-8) is recommended.

The DASDONLY(YES)keyword instructs the System Logger to define a DASD-only Log Stream which does not require the coupling facility.

The RETPD(4) and AUTODELETE(YES) keywords instruct the System Logger to retain the log data for four days and then automatically delete it.

The STG_SIZE(12288) keyword instructs the system to create a VSAM linear data set with a size of 12,288*4096 bytes or 50 MB for staging logger records.

For DASDONLY Log Streams, staging data sets are required as part of the System Logger configuration. The System Logger automatically duplexes data to the staging data set for the system at the same time it writes the data to local storage buffers.

The LS_SIZE(36864) keyword instructs the system to automatically create VSAM linear data sets of size 36,864* 4096 bytes or 151 MBs when necessary to hold logger records as they are offloaded from the staging data set.

IBM recommends that you size the data sets as large as your installation can 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 the 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.

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.

Without directory extent records, the maximum amount of data that can be held concurrently in the Log Stream is 151 MB * 168 or 25.4 GB based on the recommended values.

Note: The sample STG_SIZE and LS_SIZE values are based on the default setting of three for the LogDetailLevel attribute. If LogDetailLevel one or two is set instead, the sample sizes can be reduced by half.

The HLQ(VTAPE) keyword instructs the system to define the staging and logger VSAM linear data sets using the a high-level qualifier of VTAPE in the data set name. We recommend that you specify a value consistent with your other Log Stream data sets that includes VTAPE. If this results in a multiple level qualifier like SYS2.VTAPE, then the HLQ parameter will need to be changed to the EHLQ parameter. HLQ(VTAPE) will need to be changed to EHLQ(SYS2.VTAPE).