A CRUSH location is the location of an OSD in a CRUSH map. For instance, an organization named mona-labs.com has a Ceph cluster with the CRUSH location of osd.156, which belongs to the host ceph-node15. This host is physically present in chassis-3, which is installed in rack-16, which is a part of room-2 and datacentre-1-north-FI.

This osd.156 will be a part of a CRUSH map, as shown in the following diagram:

In the preceding diagram, keys are shown on the left-hand side of =; these are also known as CRUSH types. The default CRUSH map includes root, datacentre, room, row, pod, pdu, rack, chassis, and host. It is not mandatory to use all the CRUSH types while defining a CRUSH map, but the used CRUSH type must be valid, else you might get compilation errors. CRUSH is quite flexible; you can even define your custom CRUSH types and use it across the CRUSH map in your own way.