If you have a machine with a ceph instance and you mount the ceph volume on the same machine, it doesn't occur automatically after booting up.
If you have ceph in extra_net_fs_list (rc.conf) and specify a mount in fstab, currently netmount starts before ceph.
A solution would be to start ceph before netmount:
# diff -u /etc/init.d/ceph.orig /etc/init.d/ceph
--- /etc/init.d/ceph.virgin 2013-01-15 16:28:53.059122604 +0100
+++ /etc/init.d/ceph 2013-02-05 12:45:16.005626713 +0100
@@ -5,6 +5,7 @@
+ before netmount
Thank you Alexey