IOS_CMRTIME_MONITOR

Description:

Detects if any control units in the system are reporting inconsistent average initial command response (CMR) time for their attached channel paths. The check issues an exception if at least one control unit in the system has a path with an average CMR time that is the highest among the other paths to the control unit and meets the following conditions:

The average CMR time for this path is greater than the THRESHOLD check parameter value.
The average CMR time for this path is significantly higher (as defined by the RATIO check parameter) than the path with the lowest average CMR time for this control unit. That is, the average CMR time for this path is at least 'x' times the lowest average CMR time for this control unit (where 'x' is the RATIO check parameter value).
Example:
```
Path 1, average CMR time = 11ms
Path 2, average CMR time = 3 ms
Path 3, average CMR time = 2 ms
Path 4, average CMR time = 4 ms
```
If THRESHOLD is 3ms and RATIO is 5, the check issues an exception because path 1 has a CMR time (11ms) that is greater than 3ms and is also greater than 5 times the CMR time for path 3 (2ms).

Reason for check:

Initial Command Response (CMR) time is a component of Response time and measures the round trip delay of the fabric alone with minimal channel and control unit involvement and thus can be a symptom of potential problems in the fabric. By monitoring this measurement alone and comparing it among the paths to a control unit, fabric problems like hardware errors, misconfiguration and congestion may be more easily detected.

z/OS® releases the check applies to:

z/OS V1R10 and later.

Parameters accepted:

Yes, the following parameters are accepted:

PARM('THRESHOLD(threshold),RATIO(x),XTYPE(devtype),XCU(cu1,cu2,...,cux)')

THRESHOLD(threshold)

THRESHOLD defines the value in milliseconds that is used in conjunction with the RATIO parameter to determine whether an exception exists. If the path with the highest average CMR time is greater than the THRESHOLD value, then the RATIO value is used to further determine if an exception exists.

A THRESHOLD value of 0 means the highest average CMR time can be any value and exceptions will be declared as defined by the RATIO value alone.

Range: 0 to 100

Default: 3

RATIO(x)

RATIO defines the value used to determine if the path with the highest average CMR time is significantly higher than the path with the lowest average CMR time for this control unit using a factor of 'x'. This is used to determine if an exception exists only after the THRESHOLD condition has been met.

If the THRESHOLD condition has been met and if the path with the highest average CMR time is at least 'x' times greater than the path with the lowest average CMR time, an exception will be declared for the control unit.

Range: 2 to 100

Default: 5

XTYPE(devtype)

devtype is the device type of control units that will be excluded from the check and not reported on.

Supported device types: DASD,TAPE

Default: no value

XCU(cu1,cu2,...,cux)

XCU defines a list of specific control units that will be excluded from the check and will not be reported on. Each control unit in this list is a hexadecimal value representing the control unit number. This parameter takes up to 40 different control unit numbers.

Range: 0 to FFFE

Default: no value

Note that if any parameter is changed, the check results may not reflect these changes for several minutes because the check must gather a few minutes worth of data before performing analysis using the new parameters.

User override of IBM® values:

The following shows the default keywords for the check, which you can override on either a POLICY statement in the HZSPRMxx parmlib member or on a MODIFY command. This statement may be copied and modified to override the check defaults:

 UPDATE
       CHECK(IBMIOS,IOS_CMRTIME_MONITOR)
       ACTIVE
       VERBOSE(NO)
       INTERVAL(00:05)        
       SEVERITY(MED)
       DATE('date_of_the_change')
       PARM('THRESHOLD(3),RATIO(5),XCU(),XTYPE()')
       REASON('Your reason for making the update')

Debug support:

No.

Verbose support:

Yes, if VERBOSE(YES) is specified on the check, the control units that were excluded via the XTYPE and XCU parameters will be displayed in the report if exceptions were found for them. This allows an easy way to temporarily obtain information on ALL control units with an exception without the need for a change to the XCU and XTYPE parameters.

Reference:

For more information on interpreting initial command response (CMR) time for the affected control units, see "IOQUEUE - I/O Queuing Activity Report" in z/OS RMF Report Analysis.

Messages:

This check issues the following exception messages:

IOSHC112E

See IOSHC messages in z/OS MVS System Messages, Vol 9 (IGF-IWM).

SECLABEL recommended for MLS users:

SYSLOW