Raid and mdstats scraper for Linux under hostmetrics

[jherbage]

Component(s)

receiver/hostmetrics

Is your feature request related to a problem? Please describe.

Migrate some Prometheus node exporter functionality not currently available in otel.

We are going through the metrics we use from that exporter which cannot be generated from hostmetrics receiver and one example are the raid and mdstats metrics.

Describe the solution you'd like

We would like the functionality, and metrics generated, in this exporter code to be available in otel's hostreceiver as a seperate linux-only scraper.

https://github.com/prometheus/node_exporter/blob/master/collector/mdadm_linux.go

Describe alternatives you've considered

None available

Additional context

N/a

[github-actions]

Pinging code owners:

• receiver/hostmetrics: @dmitryax @braydonk

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[braydonk]

I support adding this scraper (though I see this as a potential slippery slope of just adding scrapers for every kind of filesystem which could get unruly, but I can't think of a better way to handle that yet).

Over in #39978 we are also adding a nfsscraper. That setup is going to be very similar to this one. Would you be willing to follow the process I set out in this comment? This includes contributing the raid metrics to https://github.com/open-telemetry/semantic-conventions along with the expectation that the System Semantic Conventions group can reach out to you or some associates for issues that come up relating to the contributed metrics.

[jherbage]

Thanks for the feedback.
This isn't a normal filesystem. I am no linux expert but this is processing multiple disk device controller stats which are written by the kernel into the virtual filesystems /proc and /sys on linux.

Happy to follow the process and strip back my PR to the barebones for an initial PR but I have finished the MR barring a few comments I need to fix around how it handles linux only and semantic guidance.
Happy to follow the guidance next time but do you want the already submitted PR stripped back to barebones on this one?

[braydonk]

I think leaving the PR that exists is fine. I do think that blocking it being merged until these metrics are submitted to Semantic Conventions first is important though.

[jherbage]

Will do Brandon. Thanks.

[jherbage]

And my PR to go with the semantics issue @braydonk
open-telemetry/semantic-conventions#2294

It wasn't clear to me based on existing hostreceiver scrapers how to map from my meatdata.yaml to the new attributes and metric names proposed other than just copy the names I proposed into meatdata.yaml as I have done now so the PR for semantics and otel contrrib are at least aligned.