Try prstat -m and check the major contributors for the % of SYS mode. I *think* the kernel mode includes the IO device wait time. /app/oracle$ prstat -m PID USERNAME USR SYS TRP TFL DFL LCK SLP LAT VCX ICX SCL SIG PROCESS/NLWP 11603 oracle 56 3.3 0.0 0.0 0.0 0.0 39 1.3 1K 73 1K 0 oracle/1 24601 oracle 11 3.6 0.0 0.0 0.0 0.0 86 0.0 160 17 6K 0 oracle/1 24599 oracle 6.2 4.1 0.0 0.0 0.0 0.0 90 0.0 138 5 5K 0 oracle/1 HTH, Dimitre