Page of GC20-1801-10 As Updated March 3, 1980 by TNL GN25-0776
Planning Considerations for Other Virtual Machines RESTRICTIONS: DEVICE SHARING BETWEEN REAL PROCESSORS I. When a device is shared between processors and at least one of the I processors is running VM/370, the shared volume cannot contain more I than one minidisk. The single minidisk may encompass the entire I volume or a small portion of the volume and the remainder of the I volume must not be referenced by CP for use as paging, spooling, I etc., or by any virtual machine. I. Devices shared between processors must not be generated in VM/370's I DMKRIO as having alternate paths. If there are multiple paths from I the VM/370 processor to the shared devices, as well as a path from I the same devices to another processor, the paths from the VM/370 I processor cannot be generated in DMKRIO as alternate paths via the I ALTCH or ALTCU macro operands. lhi§ 1hg deiini1i2n 2i I Eg!hs gng 2t RESTBICTIONS: DEVICE/MINIDISK SHARING ON A SINGLE PROCESSOR I. If more than a single path to a volume exists, DMKRIO may be I generated so that each path is defined as a separate path, not as an I alternate path. When this is done, each path can be attached or I dedicated to a different user, and reserve/release CCws issued by I such users preserve the data integrity. In this case, the integrity I is preserved by the hardware, not by the software reserve/release I support. !,gg!n, definitiQll 2t ,Eath§ in !H1!RIQ gng I of I. A volume may be defined through the Directory to contain one or more I minidisks. Such minidisks must be identified through the MDISK I statement as requesting virtual reserve/release support. These I minidisks may then be shared between virtual machines that support I Shared DASD and the data integrity is preserved by the use of I reserve/release CCWs in the virtual machine channel program. I Alternate paths may be defined to the device when using virtual I reserve/release. The reserve CCW will still be changed to a sense CCW I but the integrity will be preserved by the virtual reserve/release --.:1- ,",vue. Virtual Machine Communication Facility The Virtual Machine Communication Facility (VMCF) allows one virtual
machine to communicate and exchange data with any other virtual machine
operating under the same VM/370 system. The VKCF external interrupt
masking is controlled by PSW bit 7 and CRO bit 31. It is to a user's
advantage to always have CRO bit 31 set to 1 (while VMCF is in use) and
control the interrupts with PSW bit 7 only. This reduces the number of
LCTL instructions.
Part 1. Planning for System Generation 48.3

!1arch 3, 1980 48.4 IBM VM/370 Planning and System Generation Guide