Page of GC20-1801-10 As Updated April 1, 1981 by TNL GN25-0837 3850 MSS In this publication, the device addresses corresponding to the
channel interface positions on the Staging Adapter are referred to as 3330V device addresses. There are 64 3330V devices per channel
interface position, or 192 3330Vs per Staging Adapter. There may be
volumes mounted on all of these devices concurrently. These 3330V volumes 3330-1 volumes, and with the proper programming
support, may be used for all purposes that a 3330-1 volume is used
except VM/370 system residence, paging, and spooling. I 3330V devices may be used in three different ways in VM/370: Mounted on the device and used
system residence, paging and
control proqram.
as VM/370 system volumes (excluding
spooling) under the control of the I Dedicated to a virtual machine as a 3330-1 and accessed from the
virtual machine using standard 3330-1 I. Dedicated to a virtual machine as a 3330V, in which case the virtual
machine must contain MSS support.
A 3330V device address is not manually available to the VM/370 system
operator. Instead, it is an accumulation of pages of staging space on MSS staging DASD. Volumes are mounted on, and demounted from, 3330V devices only through orders passed to the MSC.· The MSC is supported as
a dedicated device under VM/370 and full MSC support is contained in OS/VS1 and MVS. Therefore, to mount and demount 3330V volumes for VM/370 use, the control program communicates with an as/vs system to
which an MSC channel interface is dedicated.
Any programming in a virtual machine that accesses a real 3330-1 can
access a 3330V without modification. One or all CMS users may access CMS minidisks on MSS volumes. One MSS 3330V volume may contain the
minidisks for one or many CMS users., At the same time, virtual volumes
may also be used as system residence packs for a VS system, and the VS system can be IPLed from the virtual volume.
The mounting and demounting of 3330V volumes used as VM/370 system
volumes is accomplished by the control program communicating with an OS/VS system in a virtual machine. There is an MSS communication
program named DMKMSS which is part of the VM/370 system, but which runs
in supervisor state in an OS/iS1 or MVS system. This DMKMSS program is
the interface between the VM/370 control program and the MSC support
contained in OS/VS. The steps to install-DMKMSS in an OS/VS system are
listed in the section "Generating CP and CMS Using the starter System" later in this publication.
It is not necessary to generate a VS operating system specifically
for the virtual machine environment. Any OS/VS1 or MVS system that
supports the MSS can utilize VM/370 MSS support, and can act as the host
for the communicator program. There is, however, a requirement for the MSS I/O devices in the VS system to match the definition of the virtual
machine. When OS/VS is IPLed, the system tests for any 3330Vs that are not
online. When one is found, an order is issued to the MSC for demount.
In essence, the 3330V address is passed to the MSC and the order tells
the MSC to demount any volumes currently mounted on that 3330V. A 3330V may be offline to a virtual machine because none of VM/370's 3330Vs were allocated to the virtual machine at that virtual address.
However, the 3330V may be a valid address to the MSC. If the virtual
machine issues a demount order to one of these 3330V devices, a volume
in use by VM/370 or another virtual machine MSC can be demounted.
Part 1. Planning for System Generation 73
--- - -...l ---- ----- ---"' 3850 MSS Therefore, the following rule must be used when defining (via IOGEN) 3330V devices in a VS system to run in a virtual machine to which an KSC in ter face is dedicated.
For each 3330V defined in the VS system there must be a corresponding 3330V defined to VM/370 and allocated to the virtual machine.
For example, if you wish to dedicate real 3330Vs 240 through 27F to
virtual CPUID 22222 as virtual devices 140 through 17F, then only 3330Vs 140-17F can be defined (via IOGEN) in the OS/VS system running in CPUID 22222. I SPECIAL CONSIDERATIONS FOR THE VS1/VS2 CENTRAL SERVER VIRTUAL MACHINE At detach time, the VM/370 control program destages changed cylinders on a'volume when the use count for the entire volume reaches zero. The
destaqe function is accomplished by a relinquish order to the MSS throuqh the central server. A relinquish order iR for volume-IDs mounted on SYSVIRT and VIRTUAL virtual unit addresses
which have had a volume mounted on them by VM/370 on behalf of the guest
operating system. No data are destaged for VIRTUAL units that were not
mounted by VM/370. The following VS1/VS2 APARs must be applied to the central server
virtual machine operating system when VM APAR 11344 (relinquish
function) is applied to the VM/370 control program. The following APARs
should be applied regardless of whether the new function is desired: COMEQNENT SC.1]] SC1CI SC1DP VS1 APAR OX27455 OX27456 OX27453 OX27454 VS1 SPE BASE UX90058 UX90059 UX90054 UX90056 VS1 SPE MSSE UX90055 UX90057 VS2 APAR OZ49650 OZ49655 OZ49642 OZ49643 VS2 SPE BASE UZ90134 UZ90135 UZ90130 UZ90132 VS2 SPE MSSE UZ90131 UZ90133 VM/370 APAR 11342 permits general use volume sharing on 3330 virtual
unit addresses between a VM/370 system and a native VS1/VS2 system when
the unit control blocks are not generated in the VS1/VS2 central server
virtual machine. The following VS1/VS2 APARs must be to the
central server virtual machine operating system when this fUnction is
desired: VS1 VS2 APAR PTF APAR PTF OX24117 UX15678 OZ48289 UZ33530 If general use volume sharing is not desired, these APARs do not
have to be applied.
74 IBM VM/370 Planning and System Generation Guide
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