If applications use asynchronous I/O on filesystem files, the OS uses the AIO subsystem. The number of AIO servers to start per CPU and the number of requests each server fills can be tuned with the smit fastpath “aio”. I usually set the number of request to 8192.
To see the current number of AIO server running:
pstat -a | grep aios | wc -l
If the number of AIO servers running is at or near the maximum (maxservers * # of cpus in 5.3), increase the minimum and maximum number of AIO servers in smit.