Page of GC20-1801-10 As Updated March 3, 1980 by TNL GN25-0776 Planning Considerations for Other Virtual Machines
If any I/O devices controlled by VM/370 for its own exclusive use are
attached to a control unit with a two-or four-channel switch, the
processor controlling the other channel interface must vary the CP-owned devices offline. For example, if all eight disks in the preceding
configuration are mounted and two of those disks are CP-owned volumes
(such as CP system residence and CP paging and spooling volumes), the Os system running on PROCl must vary the CP-owned volumes offline. This
procedure protects volumes that CP needs. You can also use the Two-or Four-Channel Switch for devices attached
to one processor that is running VM/370. For example, one processor
could be running VM/370 with as running in a VM/370 virtual machine as
shown in Figure 6. In this case, the virtual machine operating system
supports channel switching. PROCl r I i .J r- ----, I VM/370 I t- I I t I I 10SI '--___ .J
, I -_._- -, - -- 2-
Channel Switch I I f-·----+-----+------+------I I I I I , I I , I , .1. __ . __ --.L ____ -.J I L ____________ ---.J Figure 6. Channel Switching on One Processor 290-297 390-397 VM/370 requires the following RDEVICE and RCTLUNIT macros to support
this configuration: RDEVICE ADDRESS=(290,8) ,DEVTYPE=2314 RDEVICE ADDRESS=(390,8) ,DEVTYPE=2314 RCTLUNIT ADDRESS=290,CUTYPE=IFA RCTLUNIT ADDRESS=390,CUTYPE=IFA For this example, you should have all the devices associated with one
path offline when you load Otherwise, the following message is
displayed: DMKCPI954E DASD raddr VOLID volid NOT MOUNTED, DUPLICATE OF DASD raddr
The 2314 DASD devices can be used by the OS system running in a
virtual machine if they are dedicated to that virtual machine via the
ATTACH command or the DEDICATE control statement in the VM/370 directory. The device addresses generated for the virtual machine
operating system need not be the same as those defined for the real
machine. As another example, consider channel switching for tapes. If the
real configuration includes a 2816 Switching Unit or a Two-or
Four-Channel Switch Feature, it can be made to operate under control of
a virtual machine operating system. For example, if 580 and 680 are the
alternate device addresses for a particular tape drive, then: Generate the virtual machine operating system for the appropriate
hardware (in this case a 2816 Switching Unit on channels 5 and 6).
44 IBM VM/370 Planning and System Generation Guide
Page of GC20-1801-10 As Updated March 3 r 1980 by TNL GN25-0776
Planning Considerations for Other Virtual Machines Generate CP as though 580 and 680 are different devices (with
different control units and channels) Issue the CP ATTACH command for both device addresses (580 and 680)
whenever the real device is to be attached to the virtual machine. The device addresses generated for the virtual machine operating
system do not need to be the same as those on the real machine.
The devices must be used by
(a ttached r or def ined wi th
directcry) the virtual machine as dedicated devices
a DEDICATE statement in the VM/370 VM/370 alternate path logic provides support for the two channel switch r two channel switch additional feature r and the string switch
feature. The purpose of alternate path support is to define alternate
paths to a given device on the VM/370 processor. The virtual operating
system does NOT define alternate paths. Instead r VM/370 would define
alternate paths to the device by the RCTLUNIT and RDEVICE macros r respectively. VM/370 would then perform the alternate path I/O scheduling. Using Figure 6 r if the installation wanted VM/370 to
perform the alternate path I/O scheduling instead of the virtual
operating system r the following RDEVICE and RCTLUNIT macros would be
required: RDEVICE ADDRESS=(290,8) rDEVTYPE=2314 RCTLUNIT ADDRESS=290,CUTYPE=IFA r ALTCH=(3) RCHANNEL ADDRESS=3 RCHANNEL ADDRESS=2 Channel-Set Switching Facility The channel-set switching facility is a feature available on the 3033
attached processor system. This feature permits a set of channels to be
switched from one processor to another in a multiprocessor or attached
processor environment. A channel-set is the collection of channels that
are switched as a group. On a 3033 attached processor system r all
online channels comprise the channel-set.
The switching operating directs the execution of I/O instructions and I/O interruptions from the main processor to an attached processor, thus
permitting an operator to vary the main processor offline. The
switching operation does not control other channel activity, such as
data-transfer operations and chaining.
In 3033 attached processor channel-set switching is
used to continue system operation in uniprocessor mode when the main (I/O) processor is taken offline as the result of a VARY PROCESSOR OFFLINE command or a main processor failure. This support switches the
channel-set from the main processor to the attached processor.
There are no required system generation macro instructions to support
channel-set switching. In the event of a failure on the main (I/O) processor, trre automatic processor recovery routine determines if
channel-set switching capability exists. If there is no channel-set
switching capability in the system r CP enters the wait state with a wait
state code of X'OOOl'. If the error is TaD clock damage and the
processor is in problem state and equipped with the channel-set
switching facility, the I/O processor is taken offline. The channel-set
switching feature is used to disconnect the channel-set from the failing I/O processor and to reconnect the channel-set to the attached
processor. The system continues processing on the attached processor in
uniprocessor mode. Part 1. Planning for System Generation 45
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