Naming conventions for the log stream and DASD data sets

For each coupling facility and DASD-only log stream you plan, do the following:

Determine the log stream name.
A log stream name should be a unique descriptive identifier, made up of one or more qualifiers (each 1 to 8 characters in length) separated by periods, up to the maximum length of 26 characters. IBM® recommends that the log stream name match the installation's data set naming conventions, with user ID or system logger application name as the first qualifier. This will simplify reporting, defining RACF® generic profiles, and writing SMS ACS routines.

It is also recommended that, when possible, one qualifier in the log stream name should be variable, to distinguish between instances used by the application writing to the log stream. To use this naming method effectively, specify a different variable name to define a different instance of a log stream for use by the application. For example, a valid log stream name for one instance of a system logger application named LOG1 might be LOG1.instance1.RECOVERY. Another instance of that system logger application may have a log stream named LOG1.instance2.RECOVERY. Make sure that each instance of the application has a mapping of which log stream resource name it should be using. The variable names and the log streams they represent need to be provided to the application as part of the application's initialization or setup.
Use the following rules in naming a log stream:
- Each qualifier can contain up to eight numeric, alphabetic, or national ($, #, or @) characters.
- The first character of each qualifier must be an alphabetic or national character.
- Each qualifier must be separated by periods, which you must count as characters.
See Sysplex requirement for information related to logstream names in environments with multiple sysplexes in a GRS Ring complex.
Determine the high-level qualifier for log stream data sets.
Define either a high-level qualifier (hlq) or an extended high-level qualifier (ehlq). The high-level qualifier will be used in the DASD log data sets and DASD staging data sets for each log stream.
For example, depending on the needs of your installation, you could set the high-level qualifier to one of the following:
- Sysplex name
- Subsystem group name
- System logger application type name
The extended high-level qualifier is similar to the high-level qualifier, but it provides more flexibility to help meet the installation's naming conventions for log stream data sets. The active primary LOGR couple data set must be formatted at a z/OS® Release 1.2 level in order to specify an extended high-level qualifier. The maximum length of the extended high-level qualifier, including periods, is 33 characters. However, the overall log stream data set names cannot be greater than 44 characters.

The high-level qualifier and the extended high-level qualifier are mutually exclusive and cannot be specified for the same log stream definition. When the ehlq is not specified, the resulting high level qualifier for the log stream data sets is based on whether hlq or the LIKE parameter is specified. If the HLQ parameter is specified, then that value will be used for the log stream data sets. When no high level qualifier is explicitly specified, but the LIKE parameter is specified, then the high level qualifier value being used in the referenced log stream will be used for the newly defined log steam. If the extended high-level qualifier, high-level qualifier, and LIKE parameters are not specified, then the default value IXGLOGR is used.

System logger does no SAF authorization checking for the high level qualifier you select for the DASD log data sets. This means that while you can select any high level qualifier you like, you should also plan carefully the name you choose. For example, system logger will allow you to choose SYS1 as your high level qualifier, but your DASD log stream data sets will end up in your master catalog! IBM recommends that you plan your high level qualifier carefully and add an alias for each high level qualifier in the master catalog that points to a user catalog.

System logger uses the log stream name to generate the DASD log data sets and staging data sets:

To form the log data set name, system logger combines the log stream name and the high-level or extended high-level qualifier, adding an automatically generated sequence number to form the log data set name. This combination of high level qualifier and log stream name must be unique within the sysplex.
The sequence number generated by the system consists of an 8-character string of numbers, letters, or both. You cannot try to predict or depend on the format in locating log stream data sets.

The log data set name is the name you use with SMS to manage the log data sets on DASD.
The following is an example of the log data set that is allocated when log stream name LOG1.AFORWARD.RECOVERY is defined without a high level qualifier:
```
IXGLOGR.LOG1.AFORWARD.RECOVERY.A0000001
```
Note that system logger has added the default high-level qualifier, IXGLOGR.
The following is an example of a log data set that is allocated when log stream name LOG1.AFORWARD.RECOVERY is defined with a high-level qualifier of PROD.
```
PROD.LOG1.AFORWARD.RECOVERY.A0000002
```
The following is an example of a log data set that is allocated when log stream name LOG1.AFORWARD.RECOVERY is defined with an extended high-level qualifier of MY.PREFIX.
```
MY.PREFIX.LOG1.AFORWARD.RECOVERY.A0000002
```
To form the staging data set name for a connection, system logger does the following:
For a coupling facility log stream, system logger combines the high-level or extended high-level qualifier defined for the log stream plus the log stream name and the system name derived from the IEASYSxx parmlib member. See z/OS MVS Initialization and Tuning Reference for a description of IEASYSxx.
For example, a staging data set defined on system MVS1 with high level qualifier IXGLOGR and associated with log stream LOG1.AFORWARD.RECOVERY will have the following name:
```
IXGLOGR.LOG1.AFORWARD.RECOVERY.MVS1
```
System logger cannot use a system name that starts with a digit as a qualifier in a staging data set name. Therefore, if your system name begins with a digit, system logger uses 'STG' plus the last 5 significant characters of the system name to form the low level qualifier for the staging data set name. If your system name begins with a digit, you must make sure that the last five significant characters will identify the system uniquely within the sysplex. The following examples show how system logger converts a system name starting with a digit to a low level qualifier for a staging data set name:
- System name 1SYS starts with a digit and has less than five characters. System logger converts the digit to 'STG' and adds the four characters to come up with STG1SYS for the low level qualifier for the staging data set.
- System name 1SYSTEM starts with a digit and has more than five characters. System logger converts the digit to 'STG' and uses the last five significant characters to come up with a staging data set low level qualifier of STGYSTEM.
- Systems 1SYSTEM and 2SYSTEM both start with a digit and have more then 5 characters. Unfortunately, this results in identical low level qualifiers of STGYSTEM for both system's staging data set names. You might need to change the system name specified on IEASYSxx.
For a DASD-only log stream, system logger combines the high-level or extended high-level qualifier defined for the log stream, plus the log stream name and the sysplex name taken from the COUPLExx parmlib member. See z/OS MVS Initialization and Tuning Reference for a description of COUPLExx.
For example, a staging data set defined on system MVS1 in sysplex PLEX1 with high level qualifier IXGLOGR, and associated with log stream LOG1.AFORWARD,RECOVERY will have the following name:
```
IXGLOGR.LOG1.AFORWARD.RECOVERY.PLEX1
```
System logger cannot use a sysplex name that starts with a digit as a qualifier in a staging data set name. Therefore, if the sysplex name specified in the COUPLExx parmlib member begins with a digit, system logger uses 'STG' plus the last 5 significant characters of the sysplex name to form the low level qualifier for the staging data set name. If your sysplex name begins with a digit, you must make sure that the last five significant characters will identify the sysplex uniquely. The following examples show how system logger converts a sysplex name starting with a digit to a low level qualifier for a staging data set name:
- Sysplex name 1PLX starts with a digit and has less than five characters. System logger converts the digit to 'STG' and adds the four characters to come up with STG1PLX for the low level qualifier for the staging data set.
- Sysplex name 1SYSPLEX starts with a digit and has more than five characters. System logger converts the digit to 'STG' and uses the last five significant characters to come up with a staging data set low level qualifier of STGSPLEX.
- Sysplexes 1SYSPLEX and 2SYSPLEX both start with a digit and have more then 5 characters. Unfortunately, this results in identical low level qualifiers of STGSPLEX for both systems' staging data set names. You might need to change the sysplex name specified on COUPLExx.
When a log stream resource is renamed, it will affect the names of all the original log stream log data sets and staging data sets. See the NEWSTREAMNAME keyword in UPDATE LOGSTREAM keywords and parameters of Administrative data utility for a description of how the log stream (offload) and staging data sets are handled when a log stream is renamed.