Create a Hybrid Origin+Cache for Notre-Dame

[williamnswanson]

Pelican Service:

• Client
• Plugin
• Registry
• Director
• Origin
• Cache
• Other (please give the detail)

Bockelman floated the idea of a Hybrid Cache+Origin that could pull from objects stores, but also be cached by in turn, instead of always being pulled from directly. This would help make better use of the large about of (Hard, spinning) Disk the Notre Dame Cache currently has to prevent things like egress costs from Object Stores, but also avoid the speed / throughput penalties associated with having a Cache on HDD.

I think it would be something along the lines of using one or more Origins as the Object stores for a Server that also has local caching / evicting?

Freshdesk ticket: https://opensciencegrid.freshdesk.com/a/tickets/80759

[jhiemstrawisc]

@bbockelm hoping you can weigh in here. Is there a design doc with more details? This issue seems more like it'd belong in an XRootD plugin repo, and I'm at a loss for how I'd get started with it. @patrickbrophy has mentioned a similar feature for S3 Origins, but I don't know how these pieces fit together.

[bbockelm]

The basic concept is to land the work to use XrdClS3 (Patrick was assign that IIRC) as the approach for S3 at the origin. If that pans out, then we have S3 working at the PSS layer (proxy, no caching). It's then a change in the configuration to go from PSS (no PFC) to PSS+PFC.

So... according to theory, if we can get the XrdClS3 working right, then indeed all the remaining is just config file generation.

[jhiemstrawisc]

Thanks for the update. I'll leave this issue open to track the new configuration we need in Pelican, while #2581 appears to track the actual creation of the backend. That being said, I suspect that an E2E solution for #2581 will still need the new Pelican configuration, so any PR will probably end up closing both.