Remove the space in your mounts line between commas. Either usbmoded or the driver is treating the blank character as a file/device and then your second partition is treated as another argument to the driver's insmod/modprobe and ignoring it.

Do modinfo g_file_storage and you'll see the proper syntax for the driver itself. You'll see what I mean. I inserted a space in my usb-moded.ini and got two disks detected by Windows. The first disk had a partition while the second one was just empty (due to Linux exposing a device with name ' ' to Windows I assume.

Here is how it looks with the space between the arguments to the mounts directive in usb-moded.ini:


N950-space-in-mounts-usb by brander snaxe, on Flickr

Thus, it appears there is a second device and it is the ' ' empty device.