Page of GC20-1801-10 As Updated March 3, 1980 by TNL GN25-0776
Planning Considerations for Other Virtual Machines I. A single virtual machine running under VM/370; the virtual machine I operating system must support the channel switch feature. I. A processor running VM/370 and managing multiple paths to devices I through the VM/370 alternate path support. Refer to the section on I "Alternate Path Support" in this document for a discussion on the I VM/370 alternate path support. You can use the two-or four-channel switch for
two processors. For example, one processor could be
the ether could be running as as shown in Figure 5. PROC 1 ,..-----, I I I as l- I I '-- __ --l ------------------
devices attached to
running VM/370 and I 2 f , I I ,290- 2 97 I Channel I I I I I 390-397 Switch , I I I I , I I I I , L-r----..&.--- ____ _____ _J I PROC2 I r-------, I I I I I VM/3701----------J I I '--------' Figure 5. Channel Switching between Two Processors VM/370 requires the following RDEVICE and RCTLUNIT macros to support
this configuration: RDEVICE ADDRESS=(290,8),DEVTYPE=3330 RDEVICE ADDRESS=(390,8) ,DEVTYPE=3330 RCTLUNIT ADDRESS=290,CUTIPE=3830 RCTLUNIT ADDRESS=390,CUTYPE=3830 These macros make it possible for you to run VM/370 on PROC1 or PROC2. If you are always going to run VM/370 on PROC2, you can eliminate one
path (eliminate one set of RDEVICE and RCTLUNIT macros). Part 1. Planning for System Generation 43

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