I found the solution with help from a listserver, LINUX-390@VM.MARIST.EDU.

The problem is that I allowed the installation to use a blacklist feature for devices. This prevents Linux from allocating resources at boot time (and when a new device is defined via the 'vmcp link...' command). All devices are blacklisted unless they appear in /proc/cio_ignore.

The workaround (in my case) was to issue 'cio_ignore -r 0.0.vdev' between issuing 'vmcp link...' and 'chccwdev -e 0.0.vdev'.

vmcp link maint630 2cc 2cc read
cio_ignore -r 0.0.02cc
chccwdev -e 2cc
- access the disk as needed
chccwdev -d 2cc
vmcp det 2cc

The cio_ignore results are not persistent in that I rebooted after I accessed MAINT630's 2cc disk and it was blacklisted again after the reboot. The way to make this persistent is to add the device to /boot/zipl/active_devices.txt. The change takes effect at the next boot without the zipl bootloader needing to be rebuilt.