On Tuesday, December 16, 2025 at 02:33:33 p.m. EST, Anthony D'Atri via ceph-users <ceph-users@ceph.io> wrote:

Indeed.  I suggest, if Proxmox lets you, encoding the chassis into your CRUSH topology, even if you don't use it today. Maybe in the future you can add chassis, which would expand your CRUSH options.

root default chassis chassis1    host host1   host host2   host host3   host host4 chassis chassis2   host host5 ...

With `host` as the CRUSH failure domain, you do run the risk of a PG being placed on 3 or even 4 nodes within a single chassis, which would not be good.  A custom CRUSH rule might let you constrain so that PG placements always span chassis; those are beyond my ken.   Someone else on the list could likely help with that rarified task.

Alternately there are the shiny new MSR CRUSH rules: https://docs.ceph.com/en/latest/dev/crush-msr/ https://www.youtube.com/watch?v=JpkLPkizUt4

Thanks, I will look into that. Andrew