I am working on getting 'Average read time (ms)' and 'Average write time(ms)' from "iostat -xnp" command.

In linux there is a '/proc/diskstats" command, which gives me 'Time spent in reading millis' and 'Time spent in writing millis and 'number of reads completed', and 'writes completed'. So, i can divide 'Time spent in reading' with 'Number of reads completed' to get the average read time(ms).

To derive the similar result, i am using the below equation. Please correct if its wrong.

example output of iostat:

r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device
0.8    3.7   43.5   38.3  0.0  0.0    0.8    0.4   0   0 c0d0
0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.1   0   0 c0t1d0
0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0 c2t1d0s2

Average_time_spent_reading(ms) = number_of_reads_per_second * average_service_time(ms)/(number_of_reads_per_second + number_of_writes_per_second) .

Average_time_spent_writing(ms) = number_of_writes_per_second * average_service_time(ms) /(number_of_reads_per_second + number_of_writes_per_second)

Thanks in advance.

  • Which version of Solaris? What files do you have in /usr/demo/dtrace? – Andrew Henle Feb 29 '16 at 10:35

You can solve this with DTrace - and if you use the DTrace Toolkit (http://www.brendangregg.com/dtracetoolkit.html) you can see how it's done. Solaris 11 and later let you pkg install system/dtrace/dtrace-toolkit; I think for Solaris 10 you'd need to grab it from Brendan's website directly.

  • Hi, dtrace is a solution, but i am not supposed to use it in my code. can i derive from iostat somehow? – Venkat Teki Mar 2 '16 at 9:29
  • you'd need to use libkstat. For an example of what you can see using libkstat, find out what sd instances you have, and run a command like kstat -p -m sd -i 18 (I've got an sd18). That'll show you all the reads, writes and other useful info. – James McPherson Mar 3 '16 at 23:09
  • Just bewere, however - every time you read a kstat, the entire kstat chain for the entire kernel is traversed. – James McPherson Mar 3 '16 at 23:10

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