Thank you @Kai for the excellent explanation :)

On Thursday, March 26, 2020 at 12:41:00 AM UTC+5:30, Kai Stian Olstad wrote:
>
> On Wed, Mar 25, 2020 at 09:54:07AM -0700, Shifa Shaikh wrote: 
> > @Kia Hi, 
> > 
> > As suggested I tried 
> > 
> > item.size_total instead of item.size_available 
> > 
> >  "{{ ansible_host }}_{{ item.mount }}: {{ (100 * ((item.size_total - 
> > item.size_available) / item.size_total)) | round(1, 'common') }}" 
> > 
> > 
> > 
> > but it still gives me 22.2 % value instead of 19% 
> > 
> > Can you please let me know what's wrong and why the difference? 
>
> This is a little out of scope of this list, so I'll keep it brief. 
>
> When you create a filesystem mkfs reserve some block on the device. 
> df output available block but this value doesn't count the reserved 
> blocks. 
>
> Filesystem            1K-blocks Used Available Use% Mounted on 
> /dev/mapper/ihs_vg_yt 51466720 8790352 40038956 19% /ihs 
>
> Just to illustrate on your df output of /ihs by doing Total - Used - 
> Available should equal 0 if no blocks was reserved. 
>
> 51466720 - 8790352 - 40038956 = 82715324 
> So you have about 82.7 million 1K blocks reserved. 
>
> df uses the "Used" / ( "Used" + "Available") to calculate used 
> 8790352 / (8790352 + 40038956) = approx. 0,18002205 
>
> So a little over 18 percent which is rounded up to 19% 
>
> When you in Ansible do size_total - size_available you are including the 
> reserved blocks in used and that is why you get a higher number than df. 
>
>
> -- 
> Kai Stian Olstad 
>

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