ReadyNas 312 - External storage device is connected but the file system is not recognized

=== df -h ===
Filesystem      Size  Used Avail Use% Mounted on
udev             10M  4.0K   10M   1% /dev
/dev/md0        4.0G  753M  2.9G  21% /
tmpfs           993M     0  993M   0% /dev/shm
tmpfs           993M  3.8M  989M   1% /run
tmpfs           497M  4.1M  493M   1% /run/lock
tmpfs           993M     0  993M   0% /sys/fs/cgroup
/dev/md127      9.1T  5.4T  3.8T  59% /data
/dev/md127      9.1T  5.4T  3.8T  59% /home
/dev/md127      9.1T  5.4T  3.8T  59% /apps
/dev/sdd1        11T  9.9T  1.1T  91% /media/USB_HDD_4
/dev/sdc2        17T  362M   17T   1% /media/USB_HDD_11
=== df -i ===
Filesystem     Inodes IUsed  IFree IUse% Mounted on
udev           253417   420 252997    1% /dev
/dev/md0            0     0      0     - /
tmpfs          254087     1 254086    1% /dev/shm
tmpfs          254087   548 253539    1% /run
tmpfs          254087    28 254059    1% /run/lock
tmpfs          254087    15 254072    1% /sys/fs/cgroup
/dev/md127          0     0      0     - /data
/dev/md127          0     0      0     - /home
/dev/md127          0     0      0     - /apps
/dev/sdd1           0     0      0     - /media/USB_HDD_4
/dev/sdc2           0     0      0     - /media/USB_HDD_11

As you can see, /dev/md0 is only 21% used and the new drive is mounted to /dev/sdc2 (although the drive is currently off).

I've tried to reply to this post multiple times. Each time my reply looks like it's been accepted and then it disappears.