The SET_BITMAP_FILE ioctl currently doesn't have a compat entry, so on 
64-bit systems a 32-bit mdadm will fail:

Sep 20 16:34:52 caspian kernel: ioctl32(mdadm:8056): Unknown cmd fd(3) 
cmd(8004092b){00} arg(00000004) on /dev/md0

The fix is to build a 64-bit mdadm or apply the following patch (compile 
tested only).

--
Paul