Sometime during AIX migration/alt_clone or HMC upgrade, it can happen that RMC ID get lost or duplicated, the the rsct process is unable to re stabilize the connection.
You can reset the key and restart that service as follows:
Reset RMC unique ID:
# /usr/sbin/rsct/install/bin/recfgct
# /usr/sbin/rsct/bin/rmcctrl -z
# /usr/sbin/rsct/bin/rmcctrl -A
Then you can check the rmc status:
# /usr/sbin/rsct/bin/rmcdomainstatus -s ctrmc
When AIX will not release /dev/cd0 device (after umount any associted filesystems), and you get busy device error on dlpar operations, use this command to kill all processes that take busy resource:
# fuser -k -x -u -c /dev/cd0
Usually in pSeries hardware configuration is connected to a scsi controller by scsi-to-ide/sas/sata or other terrible solution bridge.
To made all this operation faster you can identify pci parent adapter and remove recursively all device.
Identify:
# lsdev -l cd0 -F parent
scsi0
# lsdev -l scsi0 -F parent
sisscsia0
# lsdev -l sisscsia0 -F parent
pci10
Remove:
# rmdev -Rdl pci10
cd0 deleted
ses0 deleted
scsi0 deleted
sisscsia0 deleted
pci10 deleted
Then you can move the controller from HMC to another LPAR