Specifications

66 IBM System z Personal Development Tool: Volume 3 Additional Topics
The output of the program is the file user diskmap a. This may be browsed, as follows:
browse user diskmap a
Inspecting this output, we found that volume VMCOM2 had no minidisks defined after cylinder
1666. We added the MDISK statement for user BILL and ran the mapdisk program again, as
seen in Figure 4-9 on page 67. Note the last line of the output, which verifies that we placed
BILL’s 191 minidisk where we wanted it.
After updating the user direct c file, activate this new directory; this builds a new working
directory for z/VM. The command is:
directxa user direct c
Be certain to look for any error messages.
Attempting to manage absolute cylinder addresses and ranges when defining minidisks can
appear messy and crude. It is. This is why higher-level tools such as DIRMAINT exist.
However, using these tools requires additional skills. A very small z/VM, with only a few
simple added users, can be readily managed by directly editing the z/VM directory. A few
guidelines include:
򐂰 Do not change the minidisk definitions (or paging, spooling, temporary disk space, or
directory space) for the system volumes, with the exception that you can add a few small
minidisks in empty space on volumes such as VMCOM2.
򐂰 Use the diskmap program frequently and look for overlap or gap flags. Incorrect cylinder
specifications can overlap two minidisks, usually resulting in corruption of both.
򐂰 Never allocate a minidisk on cylinder zero. (This restriction does not apply to full-volume
minidisks.)
Another document in this zPDT series of documents (Volume 4: Coupling and Parallel
Sysplex, SG24-7859) contains examples of userids and full-volume minidisks suitable for
running z/OS under z/VM.