DOS/VS RECOMMENDATIONS when generating DOS/iS to run in a virtual machine, note the following recommendations: (DOS/VS Release 34 and earlier only) When generating a DOS/VS supervisor; use 4K (the size of VM/370's pages) whenever DOS/VS recommends using a 2K boundary or a multiple
of 2K. Thus, do not use the default for the SEND macro instruction.
It causes DOS/VS to round the supervisor size to the next 2K
boundary. Instead, manually calculate the size of the supervisor and
specify a 4K boundary in the SEND macro instruction. This
specification forces DOS/VS to be loaded at the next 4K page
boundary. addresses Specify an address of-01P-in the VM/370 directory CONSOLE statement.
This specification allows the DOS/VS supervisor to run on the real
processor using the real console address of 01F. If CMS is also to be used, it uses console address 01F. In this
case, specifying 01F in the CONSOLE statement allows use of this
console with both DOS/VS and CMS virtual machines.
To use more than one DOS/VS console under V8/370 or to use a 3270 display device in display operator control mode, refer to the topic "Specifying More Than One Console in a Virtual Machine" in the "General Considerations" section of this publication. Improve performance by reducing the number of privileged instructions
that must he handled by VM/370 and virtual machine assist. Generate
a tailored DOSjVS supervisor for each virtual machine and leave out
any unnecessary options. Because VM/370 issues its own stand-alone
seek (except for 2314 disks), do not specify seek separation in the FOPT macro instruction. When using DOS/VS Release 34 (or earlier) and the computer has
block multiplexer channels, specify the block multiplexer option in
beth the PIoes macro instruction and the directory OPTICN statement. However, this specification is unnecessary when using DOS/VSE hecause block multiplexer support is standard in DOS/VSE. Generate several tailored DOS/VS supervisors, if desired, and
store them on the same DOS/VS SYSRES with different supervisor names
(such as $$A$SUPn, where n is 1, 2, 3, 4, etc.).
Perfcrmance is usually better when using several victual machines rather
than using many active partitions in one virtual machine. That is, if
there is a ccmmunications system, a batch system, and a test system, create a separate virtual machine for each one. However, to only run VM/370 part of the day and to m1n1m1ze operational differences, one
multipartition production DOS/VS machine may be preferable. Section 3. DOS/VS in a Virtual Machine 71
It is usually best to make the DOS/VS partition sizes, and therefore
the whole DOS/VS virtual machine, large enough so that all jobs run V=B. Let VM/370 do the paging.
Rotational position sensing (RPS) cannot be used with V=B partitions.
Also, avoid double CCi translation and double paging. Set RSIZE equal to the supervisor size plus the sum of all V=R partitions, plus the SVA, plus 32K.
Note: An installa tion must specify ",REAL" on the DOS/VS / / EXEC job control card. When VM/370 is the primary operating system and DOS/VS is running one or
two partitions in a virtual machine, generate DOS/VS with as few options
as pessible, farticularly when several virtual machines share the same
system residence volume. When VM/370 is not the primary operating system and DOS/VS is usually
run without VM/370, generate DOS/VS to: Be transparent to the users of the other systems Have the required number of partitions When DOS/VS is run under VM/370, POWER (POWER/VS for DOS/VS or VSR/FCWEE fer DOS/VSE) should be used with the appropriate unit record devices
that are dedicated to DOS/VS. If an installation has sufficient DASD space, let both FOWER and VM/370 spool. Generate POWER with only the options that suit the
installation's needs, but make the I/O buffer sizes as large as
possible, up to 2008 bytes. If one job step in a DCS/VS job stream
abends, it is easy to use POWER to cancel the remainder of the job
stream. To use only VM/370 spooling, an installation must manually
cancel each jcb step.
There are two methods of sharing a DOS/VS system residence voluae: Have a read/write DOS/VS system residence (SYSRES) minidisk for each DOS/VS virtual machine. Then share a read-only copy of the private
core image, relocatable, and source statement libraries. Share a read-only copy of the DOS/VS SYSBES minidisk, and have
separate read/write private libraries for each virtual machine.
Because cnly one standard label cylinder is available, all virtual machines must coordinate their use of that cylinder. Which methcd is
situation.
used depends upon each installation's specific
72 VM/370 Operating Systems in a Virtual Machine
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