CMB

CMB={option}{(option,option[,option] . . .)}

This parameter allows the installation to specify I/O device classes for which measurement data is to be collected, in addition to the DASD and tape device classes. (Measurement data is always collected for DASD and tape devices.) For each I/O device to be monitored, the system needs 32 bytes of central storage.

If your system is running on a z990 processor, or higher, the system ignores anything you have specified on this parameter. Storage is allocated for ECMBs as needed. Each ECMB requires 64 bytes of central storage. CMBs will only be used when running on a processor lower than z990.

The channel stores measurement data in the CMB on a device basis. SRM uses the measurement data to perform its device selection and I/O load balancing functions.

The operator is notified if the CMB parameter contains a syntax error (message IEA926I) or if there is insufficient storage to accommodate measurement of the specified I/O device classes (message IEA340I). In both cases, SRM will prompt for respecification of the CMB parameter. If, after respecification, storage is still unavailable for measurement of the optional device classes, measurement will be done only for DASD and tape devices. Should storage also be unavailable for measurement of DASD and tape devices, SRM marks the measurement facilities as inoperative and informs the operator that device selection and I/O load balancing will be performed without I/O measurement data (messages IEA966I and IEA340I).

Operand Descriptions: One or more of the following options can be specified:

UNITR: Specifies unit record devices
COMM: Specifies communications equipment, including the channel-to-channel adapter (CTC)
GRAPH: Specifies graphics devices
CHRDR: Specifies character reader devices
n: Specifies the sum of the number of devices that you need to measure that are not DASD or tape or other types of devices specified using the options plus the number of devices that you plan to dynamically add and measure. See z/OS HCD Planning for more information about specifying the CMB parameter.

Examples of Valid CMB Statements:

   CMB=UNITR
   CMB=(COMM,100)
   CMB=(UNITR,CHRDR,COMM,150)
   CMB=50

Value Range: n is a decimal integer from 0 through 65535.

Default Value: None

Associated Parmlib Member: None