iowait question

[mtrainaky]

We are having a performance problem with one of our servers, and when I read the output from sar it appears the %iowait is high. But when I look at individual cpu's, the %iowait is fine. Can someone tell me why the Average %iowait is so high, but individual cpu's are fine? Thanks!


CPU %user %nice %system %iowait %idle
all 23.70 0.00 31.08 45.21 0.00
0 0.10 0.00 0.03 0.00 99.87
1 0.29 0.00 0.07 0.13 99.52
2 0.03 0.00 0.07 0.07 99.82
3 0.10 0.00 0.23 0.03 99.65
4 0.05 0.00 0.42 0.63 98.90
5 0.03 0.00 0.09 0.47 99.41
6 0.02 0.00 0.00 0.00 99.98
7 0.07 0.00 0.02 0.01 99.89

[coopstah13]

that is interesting, check the output of vmstat or iostat

vmstat -n 1 10
iostat -d -x 1 10

[mtrainaky]

Thanks. I should have mentioned that I've used those commands but the wait time shows also very low. I just can't understand why the %iowait average using sar shows so high but the other commands don't verify this. The other thing is that the high iowait times do seem to coincide with system responsiveness.