Cephfs : cannot mount external ceph cluster with non root path

[kifeo]

I try to mount an external ceph cluster with cephfs for backups.

I can mount the cephfs with a path capability of /, but not with a /some/path

It gives me a :
Feb 04 14:19:32 proxmox-bl2 kernel: libceph: client1148949 fsid dc87f194-4577-11ed-b69c-3cfdfeafecb8
Feb 04 14:19:32 proxmox-bl2 mount[3466036]: mount error 13 = Permission denied

The only thing that changes during the two is the mds path capability in the auth on the external ceph cluster.

Has anyone managed to do it ?

Thanks