iotop and ionice -p show a different class/priority for the same process

After running ionice -c2 -n7 on an I/O-intensive process (VirtualBox VM) and checking the result with ionice -p it shows best-effort: prio 7 which is expected. But when monitoring the overall disk I/O of all processes via iotop it shows in PRIO column a value of be/4 for that process, which I assume means **b**est-**e**ffort and level (priority) 4, which is average priority and not expected. Can somebody comment why there's a difference between what ionice and what iotop displays? And is there another way to verify the actual I/O priority of a given process other then with ionice -p ? From what I understood, there's /proc//io but it only displays bytes/characters read and written, but not the priority, cf. Know which process does I/O without iotop Also How do I view the IO priority of a process? only lists ionice -p For completeness sake, this is on RHEL 6.7 with iotop 0.3.2, and the scheduler is the default CFQ.