“Hot I/O” refers to a hardware malfunction that causes repeated,
unsolicited I/O interrupts. If such I/O interrupts are not detected,
the system can loop or the system queue area (SQA) can be depleted.
IOS tries to detect the hot I/O condition and perform recovery before
the system requires a reIPL.
When the number of repeated, unsolicited I/O interrupts reaches
the threshold value defined in the HIDT, IOS assumes that there is
a hot I/O condition and proceeds to perform recovery actions. Recovery
actions taken for a “hot” device depend on the type of device and
its reserve status.
Table 1. HOTIO
Parameters| Device |
Non-ESCON |
ESCON® |
|---|
| Reserved |
Not Reserved |
Reserved |
Not Reserved |
|---|
| DASD or dynamic pathing device |
DFLT112 |
DFLT111 |
SDFT112 |
SDFT111 |
| non-DASD and non-dynamic pathing device |
-- |
DFLT110 |
-- |
SDFT110 |
You can use HOTIO statements in IECIOSxx to modify the HIDT, and
to eliminate operator intervention where recovery actions defined
in the HIDT (by default) require the operator to respond to a message.
Note: To cancel hot I/O processing (that is, to have no detection
and no recovery from hot I/O conditions) specify 0 for the device
threshold value — DVTHRSH=0.
- HOTIO DVTHRSH=ddddd
- Specifies
the device threshold for unsolicited I/O interrupts, which must be
reached for hot I/O recovery to begin.
Value Range: 0-32767
Default: 100
- DFLT110=(options)
- Specifies
the recovery action to be taken for a non-DASD, non-dynamic pathing
device. (For the recovery actions that can be specified as options,
see Options for HOTIO recovery.)
Default:
(BOX,BOX)
- DFLT111=(options)
- Specifies
the recovery action to be taken for a DASD or a dynamic pathing device
that is not reserved or assigned. (For the recovery actions
that can be specified as options, see Options for HOTIO recovery.)
Default: (CHPK,BOX)
- DFLT112=(options)
- Specifies
the recovery action to be taken for a DASD or a dynamic pathing device
that is reserved or assigned. (For the recovery actions that
can be specified as options, see Options for HOTIO recovery.)
Default: (CHPK,BOX)
- SDFT110=(options)
- Specifies the recovery action to be taken for a non-DASD, non-dynamic
pathing device that is attached to an IBM® ESCON (or future)
channel path. (For the recovery actions that can be specified
as options, see Options for HOTIO recovery.)
Default: (BOX,BOX)
- SDFT111=(options)
- Specifies the recovery action to be taken for a DASD or a dynamic
pathing device that is not reserved or assigned and is attached to
an IBM ESCON (or future) channel path. (For the
recovery actions that can be specified as options, see Options for HOTIO recovery.)
Default: (CUK,BOX)
- SDFT112=(options)
- Specifies the recovery action to be taken for a DASD or a dynamic
pathing device that is reserved or assigned and is attached to an IBM ESCON (or future) channel path. (For the recovery actions
that can be specified as options, see Options for HOTIO recovery.)
Default: (CUK,BOX)
- BOX_LP=(device_classes)
- Specifies which
device classes should be boxed instead of performing channel path
recovery when all of the following conditions are true:
- the device is defined on the CHPID being recovered.
- either all of the device's paths are undergoing
recovery or this is the only path to the device.
- the device is currently reserved or assigned.
The device classes you can specify for BOX_LP
are DASD, TAPE, UREC, COMM, CTC, and GRAF. You can also specify:
- NONE, to turn off BOX_LP processing for all device classes.
- ALL, to turn on BOX_LP processing for all device classes. ALL
is the recommended setting.
Default: (ALL)