Minidisks Note! On a 3330, 3340, or 3350, an OS/VS, or OS minidisk must start at real cylinder 0 unless the VTOC is limited to one track. See the list
of restrictions "Appendix F: VM/370 Restrictions" for more
information and explanation of3330/3340/3350 restrictions.
MinidiskSpace Allocation OS bases all of its space allocation parameters on the volume table of
contents(VTOC) label written on each disk; it determines the amount of
space available on that volume from the format-5 (space accounting) data
set control block(DSCB). Thus, for OS to support minidisks, a VTOC must be written whose format-5 DSCB reflects the desired size of the
minidisk. The remainder of the disk space on the real disk appears toOS to be permanently dedicated, and not assignable by the OS space
accounting routines. The IBCDASDI service program should be used to
format minidisks for use byOS or DOS. A DASD volume containing multiple minidisks contains some tracks in
which the cylinder address in the count fields of recordsRO and R1 do
not agree with each other. If an attempt is made to read this volume by
IEHDASDR, you may get messages IEH8l3I or IEH869I. To prevent this,
initialize the disk with theFORMAT function of IEHDASDR before using
it. This function rewritesRO and R1 on each track so that the count
fields agree with each other.DOS space allocation is specified in the EXTENT job control card. It
is your responsibility to see that the EXTENT cards refer to valid
minidisk cylinders.On a 2314 or 2319 volume, the last cylinder of any
minidisk initialized by IBCDASDI is always reserved for use as an
alternate track cylinder. Therefore, aDOS minidisk on a 2314 or 2319,
must have a minimum of two cylinders. For example, if you are
specifying a ten-cylinder minidisk, the EXTENT card must refer to
cylinders0 through 8 only. This leaves the last cylinder for alternate
track assignment. However, on a3330, 3333, 3340, or 3350 minidisk,
IBCDASDI does not reserve a cylinder for alternate tracks within each
minidisk. Therefore, a ten-cylinder minidisk must be defined in the
EXTENT card as cylinders0 through 9. A minidisk always begins at virtual cylinder zero. Its minimum size
is one cylinder unless it is located on a 2314 or 2319 disk and is
formatted by the IBCDASDI service program; in which case, the minimum
number of cylinders is two and the second cylinder is used as the
alternate track cylinder. Except for the3350, which can be used in 3330-1 or 3330-11 compatibility mode or in native mode, a minidisk must
exist on itsreal counterpart, that is, a virtual 3340 minidisk must
reside on a real3340. When minidisks are defined on MSS 3330V volumes, the minidisks are
virtual3330-1 disks. The presence of the MSS and 3330V system volumes
is transparent to a virtual machine accessing minidisks.VM/370 controls the boundaries of minidisks. If an attempt is made
to refer to aDASD address outside the boundaries specified in the MDISK directory statements, CP presents a command reject (seek check) IIO error to the virtual machine. If the cylinder addresses in the MDISK statements inadvertently
overlap each other, the integrity of data in the overlapped cylinders
may be compromised with no error indicated.Part 1. Planning for System Generation 97
of restrictions
information and explanation of
Minidisk
contents
space available on that volume from the format-5 (space accounting) data
set control block
minidisk. The remainder of the disk space on the real disk appears to
accounting routines. The IBCDASDI service program should be used to
format minidisks for use by
which the cylinder address in the count fields of records
not agree with each other. If an attempt is made to read this volume by
IEHDASDR, you may get messages IEH8l3I or IEH869I. To prevent this,
initialize the disk with the
it. This function rewrites
fields agree with each other.
is your responsibility to see that the EXTENT cards refer to valid
minidisk cylinders.
minidisk initialized by IBCDASDI is always reserved for use as an
alternate track cylinder. Therefore, a
must have a minimum of two cylinders. For example, if you are
specifying a ten-cylinder minidisk, the EXTENT card must refer to
cylinders
track assignment. However, on a
IBCDASDI does not reserve a cylinder for alternate tracks within each
minidisk. Therefore, a ten-cylinder minidisk must be defined in the
EXTENT card as cylinders
is one cylinder unless it is located on a 2314 or 2319 disk and is
formatted by the IBCDASDI service program; in which case, the minimum
number of cylinders is two and the second cylinder is used as the
alternate track cylinder. Except for the
exist on its
reside on a real
virtual
is transparent to a virtual machine accessing minidisks.
to refer to a
overlap each other, the integrity of data in the overlapped cylinders
may be compromised with no error indicated.