ceph.conf

########### METADATA ###########
[mds]
    mds data = /data/$name

[mds.a]
    host = ceph-mds-1
########### MONITOR ###########
[mon]
    mon data = /data/mon.$id

[mon.a]
    host = ceph-mon-1
    mon addr = 172.17.200.102:6789

########### OSD ###########
[osd]
    osd data = /data/$name
    osd journal = /home/journal.$id
    osd journal size = 4096
    public network  = 172.17.200.0/24
    cluster network = 172.17.243.32/28

[osd.0]
   host = ceph-osd-7
   public addr  = 172.17.200.111
   cluster addr = 172.17.243.39
[osd.1]
   host = ceph-osd-7
   public addr  = 172.17.200.111
   cluster addr = 172.17.243.39
etc.

And on the client (wich is 10G), which IP is on 172.17.200.0/24 network :

mount -t ceph 172.17.200.102:/ /mnt/cephfs/
dd if=/dev/zero of=/mnt/cephfs/50M bs=4k count=50M ; sync