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

SET RDEVICE Unsupported Devices
3270_PRINTer
Graphics printer devices
PRINTer
Unit record printer devices
PUNch
Unit record punch devices
READer
Unit record input devices
SWITch
Dynamic switching devices
TAPe Tape devices
TERMinal
Terminals
DPS No
DPS Yes
You should specify DPS YES whenever a DASD or TAPE is being defined as
an unsupported device and it contains support for the dynamic path selection
(DPS) function: Channel Command Word (CCW) command codes X'34', Sense
Path Group Identifier (SNID), and X'AF', Set Path Group Identifier (SPID).
1362 z/VM: CP Commands and Utilities Reference
When DPS YES is specified, CP places VM’s path group identifier (PGID) in the
device’s control unit for each path to the control unit. This placement enables
the use of a single PGID for all devices connected to the control unit,
regardless of the number of guests that might be using the different devices on
the control unit, how many times a given guest is re-IPLed, or how a given
device might be shifted from one guest to another over time. A guest operating
system, such as IBM’s z/OS, has an alternate-PGID capability so it can deal
with the VM PGID on these channel paths.
When DPS NO is specified or the DPS option is not coded at all, VM takes no
action with regard to path groups or PGIDs. It is the responsibility of the guest
to which the unsupported device is dedicated or attached to form and maintain
path groups using the guest’s own PGID. The use of a guest’s PGID is often
cumbersome, if not unworkable, for DPS devices, because a PGID on a
channel path to a control unit applies to all devices connected to the control
unit, and a PGID can only be changed after clearing any previous PGID with a
system-reset of the channel path(s). NO is the default.
DPS should not be specified if the guest operating system to which the device
is dedicated or attached does not contain “alternate PGID” support.
The DPS parameter only applies to unsupported DASD and unsupported TAPE
devices. For supported devices, CP can dynamically determine whether or not a
device supports DPS at device initialization time.
RESERVE_RELease No
RESERVE_RELease Yes
RESERVE_RELEASE YES should be specified whenever a DASD is being
defined as an unsupported device and the DASD contains support for the
reserve/release function: Channel Command Word (CCW) codes X'B4', Device
Reserve (RES), X'94', Device Release (REL), and X'14', Unconditional Reserve
(UR).
When RESERVE_RELEASE is specified for an unsupported DASD, CP issues
the Device Release CCW command to the device whenever the virtual machine
to which the device is DEDICATEd or ATTACHed is reset (by the System Clear,
System Reset, or IPL commands).