Ceph
A number of users aspire to run Ceph on NixOS, and recommend varying approaches in different forums online. Here is a collection of links that can lead you along, though please consider; these experiences come from older versions of Ceph, such as v10, while (as of now) Ceph is on v19.
The Ceph Nix package has been hard-pressed to keep up with Ceph, as filesystem concerns are a larger challenge on NixOS than on other Linux lineages. Please make a Wiki account and add your experiences, if you made progress running a modern Ceph version.