You are entirely correct, Colossus isn't POSIX. However, the solution Google has, is since they control all the software, essentially everything they write acts

You are entirely correct, Colossus isn't POSIX. However, the solution Google has, is since they control all the software, essentially everything they write acts as if Colossus is their storage layer. This "solves" the persistent storage layer in a way Kubernetes cannot. Inside Google you might deploy your "Spanner" database container which knows how to interface with Colossus and doesn't require any special setup or colocation (below the cluster level). You cannot deploy MySQL on K8s and expect the same.