LOGR couple data set versioning

For general couple data set coexistence considerations, refer to Considerations for all couple data sets and Understanding couple data set coexistence.

Start of change Logger allows different format levels or functional versions of LOGR couple data sets to be defined. Certain logger functions require a specific format level of the LOGR couple data set as well as a particular release level of z/OS®. There are also minimum release levels required for all systems in a sysplex to use the different LOGR couple data set format levels. Since there are minimum release level requirements involved, there are migration, coexistence, and fall back considerations for your sysplex configuration. End of change

The following table lists the LOGR couple data set format levels, the minimum release level that systems must be running in order to use the LOGR couple data set, and the options required to establish each LOGR couple data set format level.

Table 1. LOGR CDS format levels
LOGR CDS format level	Minimum release level	Created when IXCL1DSU utility run on release level with option	Notes
HBB5520 (also referred to as the Base format level)	MVS/ESA SP520	any pre-OS/390® V1R3 release level (that is MVS/ESA SP520)	Refer to item names LSR,LSTRR.
HBB6603 (also referred to as the OS/390 V1R3 format level)	OS/390 V1R3	any OS/390 V1R3 or higher release level through OS/390 V2R10 and z/OS V1R1, z/OS V1R2, or higher release level without option NUMBER(1) for item name SMDUPLEX	Refer to additional item name DSEXTENT.
HBB7705 (also referred to as the z/OS V1R2 format level)	z/OS V1R2	any z/OS V1R2 or higher release level with option NUMBER(1) specified for the item name SMDUPLEX	If the ITEM(SMDUPLEX) NUMBER(1) specification is not provided on z/OS V1R1 or higher release level, then the default format level will be HBB6603.

The following table lists significant system logger functions and identifies the minimum LOGR CDS format level and release level requirements.

Table 2. Considerations for supporting key system logger functions
Functions	Minimum LOGR CDS format level	Minimum release level	Notes
Log streams supported in sysplex (coupling facility list structure type).	HBB5520	MVS/ESA SP520	Support for coupling facility list structure type log streams.
Managing the entry-to-element ratio (effective average buffer size) for a structure dynamically based on actual CF structure usage. Using DSEXTENT records for expanding the amount of data set directory space available for log streams (removed the 168 data set limit per log stream). Using the RETPD and AUTODELETE log stream options to aid in archiving log data and manage the amount of data kept in a log stream. Automatically allocating temporary staging data sets to safeguard log data when there is an error that leaves the only copy of log data in a volatile configuration. Associating a log stream resource manager for monitoring log data flow for recovery purposes.	HBB6603	OS/390 V1R3
Log stream type DASD-only.	HBB5520	OS/390 V2R4	Refer to DASDONLY type log stream designation.
Allow avoidance of recalling migrated log stream data sets during offload	HBB6603	OS/390 V2R8 with PTFs	Refer to log stream attribute OFFLOADRECALL.
Logger support for system-managed duplexing rebuild.	HBB7705	z/OS V1R2	Refer to log stream attribute LOGGERDUPLEX.
Allow pending updates for most log stream attributes. Extended high level qualifier (EHLQ) for log stream data sets.	HBB7705	z/OS V1R3	Most log stream attributes. Refer to log stream attribute EHLQ.
Force disconnect or deletion of a log stream. Allow DRXRC-type staging data sets.	HBB7705	z/OS V1R7	Refer to SETLOGR FORCE command and log stream attributes STG_DUPLEX, DUPLEXMODE.
Log stream production and test groups. Allowing a log stream name to be renamed.	HBB7705	z/OS V1R8	Refer to log stream GROUP attribute and update NEWSTREAMNAME.
Automatically apply log stream duplex pending updates following a successful coupling facility user-managed structure rebuild.	HBB7705	z/OS V1R10	Refer to log stream updates for attributes STG_DUPLEX, DUPLEXMODE, LOGGERDUPLEX.
Providing z/OS log stream client support.	HBB7705	z/OS V1R13 with PTFs	Refer to log stream attribute ZAI.
Providing log stream primary (interim) storage consumption alert messages.	HBB7705	z/OS V2R1	Refer to log stream attribute WARNPRIMARY.

IBM recommends you use the highest format level LOGR couple data set that can be used by the lowest system release level in the sysplex. This will allow for the latest system logger features to be available given the sysplex configuration.

For example, assume the lowest system release level in your sysplex is capable of using the HBB7705 format level version LOGR couple data set, but the sysplex is actually using a HBB6603 format level. This situation can occur when the LOGR couple data set is formatted on a release earlier than z/OS V1R12 without including the ITEM NAME(SMDUPLEX) NUMBER (1) specification. However, when the couple data set is formatted with this specification included, an HBB7705 format level version is established. When this HBB7705 format level LOGR couple data set enters the sysplex as the primary couple data set, system logger can provide all the functions as described. Therefore, in this example, it is beneficial for the installation to use an HBB7705 format level LOGR couple data set even if it does not intend to use System Managed Duplexing for the Coupling Facility structures that system logger uses.
Once a particular version of a LOGR couple data set is in use as the primary or alternate, any systems at a level below the minimum required release level for the couple data set version will be unable to access the LOGR couple data set. The inability to access the LOGR couple data set means that those systems can not exploit any LOGR function, such as updating logger inventory (policy) information or connecting to any log streams.
Once a version of a LOGR couple data set that is formatted at a higher level is brought into the sysplex, the sysplex can not revert to a LOGR couple data set that was formatted at a lower version without a sysplex-wide IPL. The sysplex will not permit a data set formatted for less capability to become the alternate LOGR couple data set.
- The following SETXCF command to identify an alternate couple data set, will be rejected if alternatedsname is not also a LOGR couple data set formatted at the same or higher functional level as the primary LOGR couple data set.
```
SETXCF COUPLE,ACOUPLE=(alteratedsname,alternatevolume)
```
- The first system that IPLs into a sysplex can not specify in COUPLExx a version of a primary LOGR couple data set that has a higher formatted level and a version of an alternate LOGR couple data set that has a lower format level. The sysplex will reject the alternate and will operate without an alternate until a version of a LOGR couple data set that has been formatted at the same or higher format level as the primary is made available as the alternate LOGR couple data set.

See Migration steps to enable system-managed duplexing of logger structures for migration steps that you must take to enable system-managed duplexing of Logger structures.