I reproduced the issue again today on z/VM (just after activating device ID 400). I started capturing the udev block events:
[...] UDEV [1259.455193] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda2 (block) UDEV [1259.470585] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda1 (block) UDEV [1259.484184] change /devices/css0/0.0.0002/0.0.0400/block/dasda (block) KERNEL[1259.489365] change /devices/css0/0.0.0002/0.0.0400/block/dasda (block) KERNEL[1259.490565] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda1 (block) KERNEL[1259.490592] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda2 (block) UDEV [1259.491521] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda2 (block) UDEV [1259.506219] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda1 (block) UDEV [1259.520112] change /devices/css0/0.0.0002/0.0.0400/block/dasda (block) KERNEL[1259.525453] change /devices/css0/0.0.0002/0.0.0400/block/dasda (block) KERNEL[1259.526714] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda1 (block) KERNEL[1259.526739] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda2 (block) UDEV [1259.527711] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda2 (block) UDEV [1259.543922] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda1 (block) UDEV [1259.557030] change /devices/css0/0.0.0002/0.0.0400/block/dasda (block) KERNEL[1259.561572] change /devices/css0/0.0.0002/0.0.0400/block/dasda (block) KERNEL[1259.562894] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda1 (block) KERNEL[1259.562922] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda2 (block) UDEV [1259.565224] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda2 (block) UDEV [1259.580456] change /devices/css0/0.0.0002/0.0.0400/block/dasda/dasda1 (block) UDEV [1259.615997] change /devices/css0/0.0.0002/0.0.0400/block/dasda (block) KERNEL[1259.620799] change /devices/css0/0.0.0002/0.0.0400/block/dasda (block) [...]
Included is a capture over a few seconds with `udevadm monitor --subsystem=block --properties --udev`
I reproduced the issue again today on z/VM (just after activating device ID 400). I started capturing the udev block events:
[...] css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda2 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda1 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda (block) css0/0. 0.0002/ 0.0.0400/ block/dasda (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda1 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda2 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda2 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda1 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda (block) css0/0. 0.0002/ 0.0.0400/ block/dasda (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda1 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda2 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda2 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda1 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda (block) css0/0. 0.0002/ 0.0.0400/ block/dasda (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda1 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda2 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda2 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda/ dasda1 (block) css0/0. 0.0002/ 0.0.0400/ block/dasda (block) css0/0. 0.0002/ 0.0.0400/ block/dasda (block)
UDEV [1259.455193] change /devices/
UDEV [1259.470585] change /devices/
UDEV [1259.484184] change /devices/
KERNEL[1259.489365] change /devices/
KERNEL[1259.490565] change /devices/
KERNEL[1259.490592] change /devices/
UDEV [1259.491521] change /devices/
UDEV [1259.506219] change /devices/
UDEV [1259.520112] change /devices/
KERNEL[1259.525453] change /devices/
KERNEL[1259.526714] change /devices/
KERNEL[1259.526739] change /devices/
UDEV [1259.527711] change /devices/
UDEV [1259.543922] change /devices/
UDEV [1259.557030] change /devices/
KERNEL[1259.561572] change /devices/
KERNEL[1259.562894] change /devices/
KERNEL[1259.562922] change /devices/
UDEV [1259.565224] change /devices/
UDEV [1259.580456] change /devices/
UDEV [1259.615997] change /devices/
KERNEL[1259.620799] change /devices/
[...]
Included is a capture over a few seconds with `udevadm monitor --subsystem=block --properties --udev`