NIM alt_disk_migration and p6 processor mode

I was trying to do a NIM alt_disk_migration on a POWER7 LPAR form AIX 7.1 to 7.2 but the nimadm scripts kept stalling, but without outputting anything interesting, even in debug mode.

In the end I gave up and tried booting the LPAR over the network to do a migration upgrade, but after picking up the kernel from the NIM server, I received this message:

   --> ERROR: This system is not supported for use with AIX 7.2. <--
   model: IBM,9119-FHB        processor: PowerPC,POWER7 (in P6 mode)


           AIX 7.2 requires the POWER7 (or later) processor.
                  This system is operating in P6 mode.

I had to power the LPAR down, go in to the saved profile and change the compatibility mode back to default:

There you go, migration upgrade running…