AIX iowait high explanation

iostat

% iowait Shows the percentage of time that the CPU or CPUs were idle during
which the system had an outstanding disk I/O request.

-> If iowait is high, it mean CPU need to wait for I/O since the disk is too busy(please also check the tmact)

vmstat

id CPU idle time.

wa CPU idle time during which the system had outstanding disk/NFS I/O
request(s). See detailed description above.

id high is ok, it mean the system it not busy

wa high is just similar to the case of iowait high in iostat.