Chapter 4. CRUSH Map Devices

To map placement groups to OSDs, a CRUSH map requires a list of OSD devices (i.e., the names of the OSD daemons from the Ceph configuration file). The list of devices appears first in the CRUSH map. When adding an OSD to CRUSH, the Ceph CLI tool will declare a device in the CRUSH map by creating a new line in the list of devices, enter device followed by a unique numeric ID, followed by the corresponding ceph-osd daemon instance.

#devices
device {num} {osd.name}

#devices
device 0 osd.0
device 1 osd.1
device 2 osd.2
device 3 osd.3

An OSD daemon maps to a single storage drive.