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How to interpret the output of 'iostat -x /dev/sdb1 20 100' ??



Hi,
 
 I'm  a newbie to tool 'iostat' and I've read the
manual for iostat several times. But it doesn't help.
I still get confused with the output of 'iostat', the
manual seems too abstract, or high-level, for me.

Let's post the output first:

avg-cpu:  %user   %nice    %sys   %idle
           5.70    0.00    3.15   91.15

Device:    rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s  
 rkB/s    wkB/s avgrq-sz avgqu-sz   await  svctm 
%util
/dev/sdb1    0.60   4.70 12.60  1.50  105.60   49.60  
 52.80    24.80    11.01     1.54   10.92   8.65 
12.20


I'll ask about the rrqm/s, r/s, rsec/s, avgrq-sz,
avgqu-sz, await, svctm and %util in the above output.

First question: How many physical disk I/O read
requests are sent to hard drive by kernel driver? is
it the subtract of (r/s - rrqm/s), or just r/s? if it
is r/s, then  it means user&sys applications send
(r/s+rrqm/s) read requests to kernel per second?

Second question: ( r/s * avgrq-sz ) is 30% bigger than
rsec/s, why? they should be equal or little difference
related to calculation omission.

Third Question: What's the UNIT of avgqu-sz, is it
NONE, or sector, or something else? If it is NONE,
then does it mean that the unit is 'read request'?

4th question: (await + svctm) is the time span for a
read request from being dispatched (by kernel driver)
to being served? If so, could we use this number as a
criteria for (disk + file_system) performance ?

5th question: %util is which percentage of CPU time?
it looks too abstract in manual, does it means (disk
I/O opertions time) divided by (%user + %nice + %sys)?
Or it is (%user + %nice + %sys) divided by all the
system time lots (%user + %nice + %sys +%idle)?

I got lost completely here, Please help.

Thanks a lot.



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