Spotted typo:
expr: |
node_filesystem_avail_bytes / (node_filesystem_avail_bytes -
(predict_linear(node_filesystem_avail_bytes*{*fstype!~"fuse.*|nfs.*"}[12h],
604800) < 0)) * 604800
And of course, I was wrong to say that disk_usage_percentage trends down to
zero - it will presumably trend up to 100 as the disk fills.
On Thursday, 18 August 2022 at 10:11:57 UTC+1 Brian Candler wrote:
> I had the a very similar requirement. It was a tricky query to build from
> scratch, but simple when you've worked it out, so I'm happy to share :-)
>
> - name: DiskRate12h
> interval: 1h
> rules:
> # Warn if rate of growth over last 12 hours means filesystem will fill
> in 7 days
> - alert: DiskFilling7d
> expr: |
> node_filesystem_avail_bytes / (node_filesystem_avail_bytes -
>
> (predict_linear(node_filesystem_avail_bytes,fstype!~"fuse.*|nfs.*"}[12h],
> 604800) < 0)) * 604800
> for: 24h
> labels:
> severity: warning
> annotations:
> summary: 'Filesystem will be full in {{ $value | humanizeDuration }}
> at current 12h growth rate'
>
> I'm using "node_filesystem_avail_bytes" rather than
> "disk_usage_percentage", but as they both trend down to zero, you should be
> able to replace it. Replace the time periods as appropriate.
>
> The logic goes something like this: say V is the variable you're
> interested in (node_filesystem_avail_bytes in this case)
>
> * we take the current value of V; call it V1
> * predict_linear(V[12h], 604800) is the expected value in 7 days time
> based on the trend over the last 12 hours; call it V2
> * filter that with < 0, so we get no value unless it's predicted to be
> below 0 in 7 days
>
> ^ V1
> | \
> | \
> +--0---x--7----> time
> \
> V2
>
> To find where the cut is on the time axis, you note that V1 is to (V1 +
> (-V2)) as x is to 7 days. That is, V1/(V1-V2) is the ratio of the lines
> V1...x and V1...V2. And therefore that's also the fraction of 604800
> seconds to the zero crossing point x.
>
> Your problem is slightly different: you want to know when the free space
> percentage will fall below 20, not when it falls below zero. I'll leave
> that as an exercise :-) I think just substituting
> (disk_space_percentage-20) everywhere in place of the variable is a good
> starting point, but you have to be careful what happens if the current
> value is already below 20.
>
> HTH,
>
> Brian.
>
> On Thursday, 18 August 2022 at 06:31:08 UTC+1 [email protected] wrote:
>
>> Hello all,
>>
>> I have the percentage of disk usage on a metric. I can use
>> predict_linear(disk_usage_percentage[30d], 30*24*60*60) to give me a
>> prediction in 1 month from the past month of metrics. fine
>>
>> but how could I retrieve the date on which the predict_linear function
>> will reach 80% for instance ? if that's possible :-)
>>
>> Thank you
>>
>> regards
>> ++ Jerome
>>
>>
>>
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