mount: /mnnt: wrong fs type, bad option, bad superblock on /dev/rbd6, missing codepage or helper program, or other error.

我用ceph挂出来磁盘，报

# map驱动
rbd device map kubernetes/ceph-bak.img

# 挂载
mount /dev/rbd6 /mnnt/

报如下错误：

mount: /mnnt: wrong fs type, bad option, bad superblock on /dev/rbd6, missing codepage or helper program, or other error.