Dear Friends ,
I am confused about iowait in linux system . Is this iowait is for Disk or CPU ?

For the below output :

output-1
---------------------
avg-cpu: %user %nice %system %iowait %steal %idle
0.27 0.00 0.83 1.51 0.00 97.39

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sda 0.08 10.68 0.26 2.60 10.90 106.27 40.87 -------------------------

output-2:
------------------------------
07:31:25 PM CPU %user %nice %sys %iowait %irq %soft %steal %idle intr/s
07:31:25 PM all 0.27 0.00 0.33 1.51 0.47 0.03 -------------------------------

Is the above 2 output , I found %iowait for CPU , but is this iowait related with Disk ?

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

https://support.hpe.com/hpsc/doc/pub...ocId=c02783994

1 members found this post helpful.

Which means it is basically useless - especially on a multicore (hyperthreaded) environment.
There are situations where it can be useful when used in conjunction with other metrics, but as a stand-alone indicator, use with care.

Appropriate Doc ...Thanks a lot..

Here I understand that CPU wait time actually interrelated with Disk IO Time .But I am confused with the below points :

1) In top command , wait% event means overall system wait time or only disk io wait time ?

2)From above redhat site :
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"So, %iowait means that from the CPU point of view, no tasks were runnable, but at least one i/o was in progress. iowait is simply a form of idle time when nothing could be scheduled. The value may or may not be useful in indicating a performance problem, but it does tell us that the system is idle and could have taken more work."
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would you please clarify about the above sentence ? Does it mean , when Disk %iowait is increasing then CPU has no new tasks for execution or, schedule to execute .CPU goes to IDLE then ?

It is not CPU wait time, nor is it disk IO time.It was probably invented to help determine why a system was idle - back in the days of uni-processor systems. As I said above, it is largely pointless in multi-processor systems.

1). see the manpage.
2). the system is idle - iowait% is a time percentage when IO is outstanding. May, or may not, be related to the tasks not running.

Why do you care ?.