When there are no z/OS system shares, it is necessary to perform all I/O to control files to a full pack minidisk. z/VM can only propagate reserve/release orders to the real DASD. You can specify CMSFP in the DDNAMES MIM file to request this type of handling. Even though this product addresses a full pack, the control file occupies only a small minidisk area on the pack, leaving the remainder of the pack free for low priority z/VM and CMS uses.
Only one control file or checkpoint file should be allocated to a single full pack. Any pack that contains a CMSFP control file should not be used for critical CP uses, such as paging or spool files, but it is acceptable to allocate user files on such a pack. When you allocate a CMSFP file, reserve space for the file by using an ordinary MDISK statement in the MIMGR user ID definition. For example, you could define control file at MIMGR 391 for six cylinders. Format the file twice, as follows:
FORMAT 391 X#1#MIM391 FORMAT 391 X 1 (RECOMP
Provide a read/write link to the same file on the full pack from where it was allocated. For example, consider the following MDISK statement:
MDISK 391 3380 1242 003 VMPK01 MW
Provide the following full pack MDISK statement, either under MIMGR or some other owner.This example is for a triple density 3380.
MDISK 591 3380 000 END VMPK01 MWV
Note: Specify END, instead of the number of cylinders, on the MDISK statement for the full pack minidisk containing the control file. For more information, see the IBM Planning and Administration manual for your z/VM system.
If the MDISK statement for the full pack is owned by another user ID include a link command under MIMGR. The user ID in this example is MAINT 123.
LINK MAINT 123 591 MW
Note: Never define two full pack minidisks addressing the same real pack. Define one, and then link to it as needed for the applications.
Once the minidisk is formatted as previous illustrated, you do not use the 391 address to perform I/O to the disk. Instead, specify the full pack address in the DDNAMES MIM file, and the absolute address, in hexadecimal format, of the first cylinder of the minidisk, as shown. In this example, the pack address is 591.
CMSFP MIMTBL01 MIM391 591 4DA
The last token, 4DA, is the hex value of the starting cylinder 1242.
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