That's not right either. On the Galaxy Nexus, there is a single /data partition. A subdirectory of this is mounted (via a FUSE gadget which enforced FAT-like semantics) for use as the "sdcard" partition, and /sdcard is a symlink to that. (It's a symlink so it can be redirected for different device users).

There is no action that can be taken on an "sdcard" partition on a GNex. It has to be done on /data.