Ah, really good question :)
I believe it is stored locally on the monitor host. Saving the cluster map into
RADOS would result in a chicken or egg problem.
This is supported by the following two sections in the docs:
1.
https://docs.ceph.com/docs/master/rados/configuration/mon-config-ref/#bac
Thank you Gregor for the reply. I have read that page. It does say what a Crush
map is and how it’s used by monitors and OSDs, but does not say how or where
the map is stored in the system. Is it replicated on all OSD, vis a distributed
hidden pool? Is it stored on the local linux disk of the ho
The CRUSH map makes up the so called "Cluster Map", for which the Ceph Monitors
maintain a master copy. This is precisely why you have multiple monitors - for
high availability in case a monitor goes down.
This is all explained quite well in the architecture documentation:
https://docs.ceph.com