fix: Memcached persistence

[AndreZiviani]

What this PR does / why we need it:
Fixes the usage of persistence on Memcached:

• Memcached must create a file smaller than disk size
• ext_wbuf_size must be bigger than max item size and be divisible by wbuf_size which is 64 by default
• Add pod permissions to access local volume

Which issue(s) this PR fixes:
Fixes #14028
Related #13619

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
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[AndreZiviani]

hey @chaudum please review this when you can

[pentago]

why is this taking ages to merge?

[eric-engberg]

I don't think ext_wbuf_size should be hard coded. Users should be able to adjust this if needed

[AndreZiviani]

I agree @eric-engberg but I could not think of a way to:

• make it configurable by the user if needed
• automatically add required options for persistency

any suggestions on how to do it?

[chaudum]

@AndreZiviani Thanks! LGMT
I will merge once the merge conflicts are resolved.

[AndreZiviani]

thanks @chaudum , done

[eric-engberg]

I agree @eric-engberg but I could not think of a way to:

• make it configurable by the user if needed
• automatically add required options for persistency

any suggestions on how to do it?

Just add it as a field in the values file. Under persistence maybe?

[chaudum]

I agree @eric-engberg but I could not think of a way to:

• make it configurable by the user if needed
• automatically add required options for persistency

any suggestions on how to do it?

Just add it as a field in the values file. Under persistence maybe?

@eric-engberg Do you want to do that in a separate PR?

[AndreZiviani]

since this is a somewhat complex and advanced usage I believe we shouldn't add any options automatically (I had some issued with this on loki-distributed helm), I've added it on previous PR because it looked like it was going to be simple but it is not

[chaudum]

@AndreZiviani Seems like the branch needs to be updated again to resolve the conflicts. I'm ready to merge then.

[AndreZiviani]

@chaudum done

[AndreZiviani]

also looks like the CI for helm release is broken
#14258

[chaudum]

Thanks @AndreZiviani !

[AndreZiviani]

release still failing btw
https://github.com/grafana/loki/actions/runs/11037391725