[collectd] question about new "disk" metrics

[Markus "Shorty" Uckelmann]

Am 16.06.2015 um 06:32 schrieb Markus "Shorty" Uckelmann:
> Am 16.06.2015 um 00:20 schrieb Gerardo Herzig:
>> Hi all. Im trying to use the "disk" metrics of the new 5.5
>> colletcd version, in order to avoid the "iostat" ruby wraper.
>> What is cool about "iostat -x" is the "disk util%", to knowing
>> how stressed the disk are.
>
>> So, it is not clear to me what maths are involved in that
>> calculations. Anyone knows if it is possible now with the new
>> disk-plugin metrics?
>
> Under Linux it should (sorry, haven't checked the code) derive from
> the iostats utility. From the man page:
>
> %util Percentage  of  elapsed time during which I/O requests were
> issued to the device (bandwidth utilization for the device). Device
> saturation occurs when this value is close to 100% for devices
> serving requests serially.  But for devices serving requests in
> parallel, such as RAID arrays and modern SSDs, this number does not
> reflect their performance limits.

Mea culpa! I just didn't read your post correctly. I can't answer your
questions.

So far I was able to find the "weighted_time" variable in the code of
disk.c. This should be the last field from /proc/diskstats which
contains the utilization as described above. But I'm not sure what
happens to this metric (my C is bad). Because it doesn't show up in
the output of the plugin.

So someone with knowledge of that plugin might jump in. I would be
interested in the disk utilisation too ;)

BTW: Some interesting links I found:

http://www.mjmwired.net/kernel/Documentation/iostats.txt
http://www.xaprb.com/blog/2010/01/09/how-linux-iostat-computes-its-results/
https://stackoverflow.com/questions/4458183/how-the-util-of-iostat-is-computed


Peace, Shorty