freebsd stable - Jun 2018 - iostat busy value calculation

On Wed, Jun 20, 2018 at 8:55 AM, Miroslav Lachman <000.fbsd at quip.cz>
wrote:
> I would like to know how the value of disk "busy" is calculated?
>
> I want to use values from iostat in the monitoring (zabbix).
> iostat shows averages by default and the last column is "busy %",
but the
> first output contains averages from the system boot til now.
>
%busy comes from the devstat layer. It's defined as the percent of the time
over the polling interval in which at least one transaction was awaiting
completion by the lower layers. It's an imperfect measure of how busy the
drives are (in ye-olden days, before tagged queuing and NCQ, it was OK
because you had THE transaction pending and it was a good measure of how
utilized things were. Now with concurrent I/O in flash devices, it's only
an imperfect approximation).

Warner

Warner Losh wrote on 2018/06/20 18:13:
> 
> 
> On Wed, Jun 20, 2018 at 8:55 AM, Miroslav Lachman <000.fbsd at quip.cz 
> <mailto:000.fbsd at quip.cz>> wrote:
> 
>     I would like to know how the value of disk "busy" is
calculated?
> 
>     I want to use values from iostat in the monitoring (zabbix).
>     iostat shows averages by default and the last column is "busy
%",
>     but the first output contains averages from the system boot til now.
> 
> 
> %busy comes from the devstat layer. It's defined as the percent of the 
> time over the polling interval in which at least one transaction was 
> awaiting completion by the lower layers. It's an imperfect measure of 
> how busy the drives are (in ye-olden days, before tagged queuing and 
> NCQ, it was OK because you had THE transaction pending and it was a good 
> measure of how utilized things were. Now with concurrent I/O in flash 
> devices, it's only an imperfect approximation).
Yes, I am aware of this issue. This percentage is just  "is it slightly 
loaded or heavily loaded" indicator.

Miroslav Lachman