Optional parameters

DVCBLOCK

Specifies the device blocking option to be applied to the volume or list of volumes in a session specified with the VOLUME parameter. The DVCBLOCK parameter is mutually exclusive with the DONOTBLOCK parameter and is ignored if you have specified SUSPENDED or XRCUTL.

Start of change Workload-based write pacing affects the behavior of DVCBLOCK. For more information, refer to Workload-based write pacing. End of change

The DVCBLOCK values are:

ON

Specifies that device blocking is enabled for the specified volume(s). This is the default unless the SHADOW DfltWritePacingLvl PARMLIB value is specified as non-zero. When DfltWritePacingLvl is non-zero, all volumes on write pacing capable storage controllers are write paced at the defaulted level unless overwritten.

Start of change When workload-based write pacing is in use, XRC automatically converts DVCBLOCK(ON) to DVCBLOCK(WPn), where n is the discretionary level, 6. End of change

OFF

Specifies that device blocking and write pacing are disabled for the specified volume(s).

WPn

Specifies that write pacing is to be activated for the specified volume(s), with n specifying the level of write pacing delay, 0-F.

WP0 specifies that the session default level will be used, as specified the SHADOW DfltWritePacingLvl PARMLIB value.

WP1-WP7 result in pacing maximums of 0.02, 0.04, 0.1, 0.5, 1, and 2 milliseconds per recordset, respectively. These levels are useful for volumes with high rates of small blocksize writes, such as data base logs, where minimal response time impact is essential.

WP8-WPC result in pacing maximums of 5, 10, 25, 50, and 100 milliseconds per recordset, respectively. These levels are useful for volumes with high mb/sec write rates.

WPD-WPF result in pacing maximums of 200, 500, and 1000 milliseconds per recordset, respectively. These levels should be used only in exceptional situations where a very high degree of pacing is required.

Delay is injected per recordset, but a write channel program might create several recordsets. In such cases, the maximum possible delay per write channel program is equal to the pacing maximum multiplied by the number of recordsets that the channel program creates. For example, at pacing level WPC, a channel program that creates 4 recordsets can be delayed for a total of 4×100, or 400 milliseconds.

There is no overall limit on the amount of delay that can be injected for a channel program. Very large channel programs, such as those used in Sort applications, can experience delays measured in seconds when higher pacing levels are used.

DONOTBLOCK

Specifies that write pacing is disabled and that the application I/O to the specified primary volumes is not blocked, even if the system data mover is unable to offload updates from the volumes rapidly enough. If you do not specify this parameter, the default is to block the primary volumes, on storage controls that support this function. This parameter is ignored if you have specified SUSPENDED or XRCUTL. You cannot use the DONOTBLOCK parameter with the DVCBLOCK parameter.

ERRORLEVEL

Specifies how the XRC session responds when an error occurs that causes the session to become unable to process a volume. You can abbreviate this parameter as ERRLVL.

Note: Suspended volumes keep the same characteristics that existed when the suspension occurred.

The error level you specify with the XADDPAIR command overrides the value that was specified in the XSTART command. If you do not specify the ERRORLEVEL parameter, the error level defaults to the value that was specified on the XSTART command.

For a volume resynchronization, you can change the error level for a volume pair from what it was prior to the suspension. XRC ignores this parameter for utility volumes or if you also specify SUSPENDED.

To specify how XRC should process certain error conditions, select one of the values:

SESSION: Specifies that, if a permanent error that is associated with a duplex primary or secondary volume occurs, XRC suspends all volume pairs in the session, regardless of the volume status. If the session is coupled to other XRC sessions, all volumes in the coupled XRC sessions are also suspended.
If you specify the SESSION parameter, volume pairs that are suspended from the session will negatively affect the usability of the remaining secondary volumes. Specify the SESSION parameter to ensure that all secondary volumes necessary for recovery are consistent up to the time of failure.

Note: To couple an XRC session to a master session, use the ERRORLEVEL(SESSION) parameter to ensure a recoverable consistency across all coupled sessions.
VOLUME: Specifies that, if a permanent error occurs, the XRC session suspends only the volume pair or pairs that are associated with the error. All other volumes continue to process.
group_name: Specifies that, if an error to a duplex primary or secondary volume occurs, XRC suspends all volume pairs that are associated with that group name. The group_name can be any name acceptable to TSO. The maximum length of the name is eight characters. Do not include embedded blanks. TSO ignores leading blanks and trailing blanks. Do not use the reserved names VOLUME and SESSION.
Note: The group_name parameter is not supported across coupled XRC sessions.

NOCOPY

Specifies that XRC add a volume pair to an XRC session without initially copying the full primary volume. XRC only copies updates to the volume after it adds the volume. This assumes that the storage administrator had previously copied the volume. XRC puts the volumes directly into DUPLEX status.

If you do not specify NOCOPY, XRC processes as follows:

XRC copies the primary volume onto the secondary volume at the same time that additional application updates are made to both copies.
Volumes are initially in PENDING status and go to COPY status when XRC selects them for synchronization.
When synchronization is complete, the volumes enter DUPLEX status.

Note: XRC ignores NOCOPY when establishing utility volumes and when resynchronizing a volume. XRC copies data to the secondary volumes during resynchronization.

FULLCOPY

Specifies that XRC make an image copy of each track of the primary volume onto the secondary volume at the same time that additional application updates are made to both copies. The volumes are initially in pending status and enter duplex state when the initial volume copy completes. FULLCOPY is the default.

Note: If you do not specify a COPY option using the XADDPAIR command, XRC uses the option that is specified on the XSET COPY command. XRC ignores the FULLCOPY option when establishing utility volumes and when resynchronizing a volume. If you do not specify an XSET COPY option, XRC uses the default of FULLCOPY.

QUICKCOPY

Specifies that XRC make an image copy of allocated tracks on the primary volume onto the secondary volume at the same time that additional application updates are made to both copies. XRC reads the VTOC of the primary volume to determine the allocated tracks on the volume. The volumes are initially in PENDING status and enter DUPLEX status when the quick volume copy completes.

XRC ignores the QUICKCOPY option when establishing utility volumes and when resynchronizing a volume.

Note: To ensure data integrity, the initial processing for QUICKCOPY must issue a reserve and then a release for the primary volume during the initial phase of the synchronization process. If access to the primary volume is through a channel extender and the connection fails while XRC has the volume reserved, applications at the primary site will not be able to access the primary volume.

SCSESSION

Specifies that XRC assign the volumes that are associated with this command to the value that you specify with storage_control_session. You can assign either one or two alphabetic characters for the storage_control_session value. If you do not specify this parameter, the default value is "--".

XRC ignores any change to the SCSESSION designation if this XADDPAIR command is resynchronizing volume pairs or if you also specify the SUSPENDED parameter. If you want to change the volume assignment, you must first issue an XDELPAIR command, then reissue the XADDPAIR command for the volume pair. This will require that you perform a full synchronization copy for the volume pair.

The SCSESSION parameter is valid for utility volumes as well as for regular volume pairs.

LOGPLUS

Specifies that the primary volume of the volume pair is to be explicitly written to by the z/OS® System Logger. When using LOGPLUS, you should specify a single pair and a utility pair, but the utility pair must be specified last. A unique storage control session number is assigned to the primary volume. If you do not specify a utility pair, any attempt to reserve the LOGPLUS volume (such as for allocating data sets) will result in a waiting for control unit condition.

LOGPLUS cannot be specified with the SCSESSION parameter. For more information, refer to Plan DRXRC-type Staging Data Sets for Coupling Facility Log Streams in z/OS MVS Setting Up a Sysplex.

Note: Overloading an individual XRC session with LOGPLUS volumes can result in degraded session performance and unacceptable application system impact. When adding high activity storage control sessions (such as those associated with LOGPLUS volumes), be sure to balance them across XRC sessions, maintaining a ratio of no more than one high activity session for every three lower activity ones within a given session.

MSGROUTEID

Specifies the user ID to which XRC messages associated with this command are routed. If the specified user ID is not logged on, TSO saves messages in the TSO BRODCAST data set and displays them after the next logon.

Note: Messages issued by the initial command syntax-checking routine are sent to the user ID that issues the TSO command.

For additional information about:

Using the NOCOPY option, refer to Adding a volume with the NOCOPY option.
Using the QUICKCOPY option, refer to Adding a volume with the FULLCOPY or QUICKCOPY option.
Using XRC utility devices, refer to Using XRC utility devices.