z/VM: CP Commands and Utilities Reference - z/VM - IBM

MODIFY DEVICE / IODEVICE
Usage Notes
NOTDASD
tells CP that this device is not a direct access storage device (DASD).
TIME_Out
tells CP that the I/O interface time out function is active for the following I/O
interfaces between the channel and I/O device:
v 4 second time out for initial selection
v 30 second time out for data transfer.
NOTIME_Out
tells CP that the I/O interface time out function is not active for this device.
PREFerred_channel_path nn
tells CP to use this channel path in the specified or implied channel-subsystem
image to initiate I/O requests before trying any other channel paths from the
device that you are changing. The variable nn must be a 1- to 2-digit
hexadecimal number between X'00' and X'FF'.
Note: A preferred path must not be specified for a device connected to a
control unit for which z/OS ® –managed paths are being used. Although
the command will not prevent you from doing so, the use of preferred
paths in a managed-path environment will adversely affect z/OS’s ability
to manage channel-path workloads.
NOPREFerred_channel_path
tells CP that there is no preferred channel path.
1. If you are using this command to modify I/O device characteristics, then you
must specify one of each of the I/O device characteristics (IODC), because this
command does not accept defaults and will not carry over any previous IODC
characteristics definitions.
For example, suppose you used the following command to define a new DASD:
define device 16d9 unit_address a3 cu 501 dasd
In this command, you specified one IODC characteristic, DASD. You took the
defaults for the other three: no preferred channel path, no status verification,
and no time out function.
If you want to change the DASD to another device and retain the previous
IODC characteristic definitions, you must specify exactly what you want:
mod dev 16d9 unit_addr a3 cu 501 nostat notdasd notime_out nopref
Note: This is especially true for DASD devices. If you are modifying the IODC
characteristics of a DASD, you must specify DASD in your command. If
you do not, the DASD will not work as expected.
2. After successfully entering this command, you will have changed the software’s
view of the I/O configuration and part of the hardware’s view: the active I/O
configuration in the hardware system area (HSA). You should also change the
other part of the hardware’s view: the active I/O configuration data set (IOCDS)
file on the support element (SE) hard disk.
To change the IOCDS file on the SE hard disk, you must:
a. Update the IOCP source file.
612 z/VM: CP Commands and Utilities Reference
b. Run the IOCP utility (see page 1849) against the updated IOCP file. If the
IOCP utility runs without errors, it downloads the new IOCDS file to the SE
hard disk.