MODIFY-IO-OPTIONS (Modify settings for I/O devices)

Using the MODIFY-IO-OPTIONS command the system support can modify the following I/O settings of the input/output devices: 

• Timeout value for I/O monitoring

Changes to timeout values are suggested for specific actions that might cause time delay in the execution of an I/O request (e.g. during the online update of RAID system’s firmware). Upon completion of these actions, the default timeout values should be restored.

• FastDPAV options for disks, if FastDPAV (s. "Parallel access volume (PAV, SU /390)") is supported in the system

In connection with FastDPAV, an additional performance improvement can be reached for disks assigned shared to the VM.
Selecting a FastDPAV alias device as preferred device for an I/O request can increase the performance additively, as the alias devices are assigned to the VM exclusively, and therefore there is no hypervisor overhead for these devices.
The setting of this option is common for all disks that are assigned shared to the respective system. 

FastDPAV devices are not available on SU x86, where the inputs/outputs are automatically parallelized by X2000. The VM2000-specific operands for prioritizing FastDPAV devices in this BS2000 command have consequently no effect on SU x86.

In VM2000 operation, the command MODIFY-IO-OPTIONS enables the modification of the options in all guest systems that support this command, if it is entered in the monitor system.

MODIFY-IO-OPTIONS                                                                                                                                          

UNIT = alphanum-name_2..2 / x-text_4..4 / *ALL / *CONTROLLER(...) / *DEVICE-RANGE(...)
	*CONTROLLER(...)
		|	NAME = <alphanum-name 2..2> / <x-text 4..4>
	*DEVICE-RANGE(...)
		|	FROM = <alphanum-name 2..2> / <x-text 4..4>
		|	,TO = <alphanum-name 2..2> / <x-text 4..4>
,TIMEOUT = *UNCHANGED / *SYSTEM-DEFAULT / <integer 16..86400>
,FAST-DPAV = *UNCHANGED / *PARAMETER(...)
	*PARAMETER(...)
		|	PREFERRED-DEVICE = *BASE-DEVICE / *ALIAS-DEVICE
,SCOPE = *OWN-SYSTEM-ONLY / *VM2000-GLOBAL

Description of the operands (VM2000-specific operands)

FAST-DPAV = *UNCHANGED / *PARAMETER(...) 
Specifies settings for FastDPAV.

FAST-DPAV = *PARAMETER(...) 

PREFERRED-DEVICE = *BASE-DEVICE / *ALIAS-DEVICE
Specifies the order of the selection of base and alias devices for the I/O execution of a VM-shared disk, if FastDPAV is supported in the system.
The setting is accepted independently of the devices specified in the UNIT operand.
If FastDPAV is not supported in the system, the command is rejected.

PREFERRED-DEVICE = *BASE-DEVICE
If no I/O is running on the base device, this one is chosen for an incoming I/O request. If an I/O is already running on the base device, a new I/O request is started on an alias device, provided there is one available. This is the system preset device selection. 

PREFERRED-DEVICE = *ALIAS-DEVICE
If no I/O is running for the device (neither on the base nor on an alias), a new I/O request is started on an alias device, provided there is one available. If there is already an I/O request running for the device, a new one will be started on the base device, if there is no I/O running on it or if no (further) alias device is available.
This device selection mode can improve the I/O performance, if there are sufficient alias devices available. It may be unfavourable, if volumes with low I/O rate occupy the alias devices and volumes with higher I/O rate have no or too few alias devices at their disposal.

SCOPE = *OWN-SYSTEM-ONLY / *VM2000-GLOBAL
Specifies how the command is to be executed in VM2000 operation.

SCOPE = *OWN-SYSTEM-ONLY
The command is executed in the local system only.

SCOPE = *VM2000-GLOBAL
If the command is entered in the monitor system, the modification of the I/O options is enabled in all guest systems that support this command. If entered in another guest system, the command is rejected.