Why load is high despite the fact that neither CPU or disk is overused

I'm getting the following output from top: Cpu(s): 43.8%us, 32.5%sy, 4.8%ni, 2.0%id, 15.6%wa, 0.2%hi, 1.2%si, 0.0%st Mem: 16331504k total, 15759412k used, 572092k free, 4575980k buffers Swap: 4194296k total, 260644k used, 3933652k free, 1588044k cached the output from iostat -xk 6 shows the following: Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util sda 0.00 360.20 86.20 153.40 1133.60 2054.40 26.61 1.51 6.27 0.77 18.38 sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 sdd 22.60 198.80 17.40 31.60 265.60 921.60 48.46 0.18 3.70 1.67 8.20 sdc 16.80 218.20 22.20 23.40 261.60 966.40 53.86 0.21 4.56 1.49 6.78 Based on the above it looks like something must be overloaded. But what? ### Questions 1. If its not the harddisk or the CPU then what? 2. It seems as though 15.6% of the CPU's time is spent waiting. What exactly could it be waiting for?