l"dge or: AS upaated April 1, 1981 by TNL GN25-0837 Minidisk Restrictions
The following restrictions exist for minidisks:
1. In the case of read home address with the skip bit off, VM/370 modifies the home address data in user storage at the completion of
the channel program because the addresses must be converted for
minidisks; therefore, the data buffer area may not be dynamically
modified during the input/output operation.
2. On a minidisk, if a ccw string uses multitrack search on
input/output operations, subsequent operations to that disk must
have preceding seeks or continue to use multitrack operations.
There is no restriction for dedicated disks.
3. as/pcP, MFT, and MVT ISAM or OS/VS ISAM running virtual=real may be
used with a minidisk only if the minidisk is located at the
beginning of the physical disk (that is, at cylinder 0). There is
no such restriction for DOS ISAM or OS/VS 151M running v iJ: t udl..;..y 1.1. t ual. 4. Because the VS1 system does no paging, any ISAM programs run
under VS1 are treated by VM/370 as though they are running in an ADDRSPC=REAL partition. VM/370 does not return an end-of-cylinder condition to
machine that has a virtual 2311 mapped to the top half
tracks 0 throuqh 9) of 2314 or 2319 cylinders. a virtual
(that is,
5. If the user's channel program for a minidisk does not perform a
seek operation, then to prevent accidental accessing, VM/370 inserts a positioning seek operation into the user's channel
program. Thus, certain channel programs may generate a condition
code (CC) of 0 on a SIO instead of an expected CC of 1, which is
reflected to the virtual machine. The final status is reflected to
the virtual machine as an interrupt.
6. A DASD channel program directed to a 3330, 3340, or 3350 device may
give results on dedicated drives which differ from results on
minidisks having non-zero relocation factors if the channel program
includes multiple-track operations and depends on a search 10 high
or a search 10 equal or high to terminate the program. This is
because the record 0 count fields on the 3330, 3340, and 3350 must
contain the real cylinder number of the track on which they reside,.
Therefore, a search ID high, for example, based on a low virtual
cylinder number may terminate prematurely if a real record 0 is
encountered.
1. Minidisks with non-zero relocation factors on 3330, 3340, and 3350 devices are not usable under OS and OS/VS systems when
the minidisk contains a VTOC of more than one track. The
locate catalog management function employs a search 10 equal
or high CCW to find the end of the VTOC. Since VM/370 does
not permit the guest to write RO, the VTOC search ends
prematurely.
7. 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. 432 IBM VM/370 Planning and System Generation Guide

Page of GC20-1801-10 As Updated April 1, 1981 by TNL GN25-0831
8. The IBCDASDI program cannot assign alternate tracks for a 3330, 3340, or 3350 minidisk.
9. If the DASD channel programs directed to 3330/3340/3350 devices
include a write record R(O), results differ depending on whether
the 3330/3340/3350 is dedicated (this includes a mini disk defined
Appendix F: V8/310 Restrictions