[ceph-users] physical vs osd performance

Hello all, Looking at grafana reports, can anyone point me to documentation that outlines physical vs osd? https://docs.ceph.com/en/latest/monitoring/ gives some basic info, but I'm trying to get a better understanding. For instance, physical latency is 20ms and osd is 200ms, these are just made up for this example, why the huge difference? Same thing if for bytes or iops, just using latency as an example. Thanks, Curt