CephFS, free space reporting

Some thoughts after weekend:

Not simply “add”, as all pools still using the same and united object space.
Instead:

  • maximum of the ( pool_raw_free / pool_redundancy_factor ) across all pools, included into CephFS.

Commonly saying, such approach will break the rule “Free + Allocated == Total”, but I’m suspecting the amount of “free” is preferrable over non-formal rules.

Also, I’m cleanly undestanding the reason of multiple data pools usage in particular CephFS. Why?
To set the different pool parameters (such as quoting / caching / replicas) in single filesystem? Why? To add more placement groups? Add them to the first pool instead… I don’t know…