Minidisks
rather than specifying ALL, which no longer dumps anything from the
final cylinders except tracks that have been assigned as alternates.
Then you can execute the IBCDASDI utility to assign alternate tracks to
the defective tracks so that all cylinders become usable. Subsequently,
the new DDR utility can be used to restore minidisks from the tape,
possibly reordering them into the previously unusable cylinders.
Note: Whenever a minidisk is moved to a new location or its size is changed, the corresponding MDISK statements in the system directory must
be revised. Only the new versions of the DDR, DIR, and FMT utilities should be
used with 3340/3344 devices after alternate tracks have been assigned. In release 6 the starter system has been changed
to reserve cylinder 348 for alternate track use. Therefore, the 3340 starter system can be restored to a disk that has defective tracks
(provided that alternate tracks have already been assigned by IBCDASDI) 2314/2319 DISKS On 2314 and 2319 devices, CP and CMS (except CMS/VSAM) do not recognize
or support alternate track techniques for their own use. DOS, OS, and CMS/VSAM minidisks, however, do recognize and support alternate tracks
on these types of DASD. The IBCDASDI service program automatically
assigns the last cylinder in any minidisk as an alternate track
cylinder. When you initialize 2314/2319 devices, you can assign all 203 cylinders for virtual machine and system use.
If a track assigned to a virtual machine minidisk area subsequently
becomes defective, you can: Run the standalone CP Format/Allocate service program if the minidisk
is used by CP, and flag the whole cylinder containing the defective
track as permanently assigned (PERM). This prevents CP from ever
allocating that cylinder for CP paging, spooling, or temporary files. You must remember not to include this cylinder when you allocate disk
space for any virtual machine's minidisk in the VM/370 directory. If the minidisk is used by either DOS, OS, or CMS/VSAM, reformat the
minidisk (including the defective track) with the IBCDASDI service
program. An alternate track is assigned at the end of the minidisk. Set up the entire volume containing the defective track as an OS, DOS, or CMS/VSAM volume and format it with either IBCDASDI or IEHDASDR for OS or CMS/VSAM disks, or with the DOS Initialize Disk
utility program (INTDK) for DOS disks. Alternate tracks are assigned
in the standard manner. Labels All disks to be handled by CP (as an entity or as a combination of
logical disks) must have a label on real cylinder 0, track 0, record 3.
This label identifies the physical volume to VM/370 and must be in the
form VOLlxxxxxx -- or -- CMS=xxxxxx where xxxxxx is a 6-character volume label. 100 IBM VM/370 Planning and System Generation Guide
Minidisks
In addition, all virtual machine minidisks should have a
virtual cylinder 0, track 0, record 3. Labels created by IEHDASDR, or INTDK
label at IBCDASDI, VOL1xxxxxx where xxxxxx is a 6-character volume label.
A physical volume that holds only virtual machine minidisks can have
the first of those minidisks starting at real cylinder O. CP recognizes
the physical volume if the first minidisk has a valid label.
In Figure 16, the volume indicated as OSDOS1 has
allocated to a minidisk that is formatted for use
serial number of that minidisk must be OSDOS1, associated with the real volume. Since the minidisk
physical volume, changing it affects the directory
who have minidisks on that volume.
its real cylinder 0 by os. The volume
the label that is
label identifies the
entries of all users You should not assign real cylinder
because that user (if he has read/write
the label on the minidisk.
o to a user as a data area,
access to the disk) can rewrite
Additionally, you must not assign user minidisks to begin on real
cylinder 0 of any physical volumes that are to contain CP controlled
areas (for paging, spooling, and so on). On these volumes, cylinder 0 track 0 record 4 contains control information required by CP. The VTOC labels written are compatible with OS, but indicate to OS that there is
no space on that DASD. The initialization programs used to format OS, DOS, and CMS/VSAM minidisks write over and destroy this necessary
control information if the space is assigned to a user minidisk, and
this causes CP system failures.
Sharing Minidisks
A minidisk can be shared by multiple virtual machines. One virtual
machine is designated the owner of the minidisk (it has an MDISK control
statement in its VM/370 directory entry describing the minidisk) and
other virtual machines can link to the minidisk.
For example, assume a virtual machine called USERA owns a minidisk at
address 150. The VM/370 directory entry for USER! contains the
following statement: MDISK 150 3330 050 010 SYS003 W READPASS USERA's virtual disk is on the volume labeled SYS003 and occupies real
cylinders 050-059. Any other virtual machine that issues the CP LINK command with the
proper password, or has the following LINK statement in its VM/370 directory entry, can read the 150 minidisk belonging to USER!. LINK USERA 150 cuu RR
The cuu is the virtual device address at which the 150 minidisk
belonging to USERA is linked to another virtual machine. If you define
another virtual machine, USERB, with the following statement in its VM/3?0 directory entry:
LINK USERA 150 151 RR Part 1. Planning for System Generation 101
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