NUMAIOVPS specifies the number of virtual processors of the AIO class to run. Unless kernel asynchronous I/O is implemented, the AIO virtual processors perform all the database server disk I/O, other than I/O to the log files.
If your platform has kernel-asynchronous I/O (KAIO) turned on, the database server uses AIO virtual processors to perform I/O only to cooked chunks. The database server uses KAIO to perform all I/O to raw disk space and to the physical and logical logs. For details, see the machine notes.