From AIXWiki

[edit] Enable aio0 (< AIX 6.1)

The aio0 device on AIX provides "legacy" asynchronous I/O support (ie. not POSIX aio). It is still used by many products, including Oracle and DB2

Use the mkdev command to determine if Legacy Asynchronous I/O is available. If the aio0 devices is in a "Defined" state, it is not configured. To verify the aio0 device:

# /usr/sbin/mkdev -l aio0.

You should see:

aio0 Available.

Enable the feature:

# /usr/sbin/chdev -l aio0 -P 
# /usr/sbin/chdev -l aio0 -P -a autoconfig=available

Reboot the system. Verify that aio0 is now Available:

# lsattr -El aio0