iostat busy value calculation

[Miroslav Lachman]

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