Freecom external USB disk shown as two different devices 2TiB and 746GiB

Question

I just bought an external USB disk called "Freecom Hard Drive XS 3TB" (user manual).

Immediately after unpacking, I plugged it into Ubuntu and it shows as two devices (/dev/sda is my laptop's drive):

The external drive is both /dev/sdc (2 TiB) and /dev/sdd (746GiB).

What I tried:

• I removed all partitions they contained, but that obviously does not make them a single /dev device.
• I created a new GPT disklabel, for each device, then restarted it. Did not work either.
• Exact same problem on a Mac made in 2013 running Mavericks.

Here is what gdisk has to say:

# gdisk -l /dev/sdc
GPT fdisk (gdisk) version 0.8.10

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/sdc: 4294967295 sectors, 2.0 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): D3C6A90D-FA52-42C0-9683-F0F599BFD5B1
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 4294967261
Partitions will be aligned on 2048-sector boundaries
Total free space is 4294967228 sectors (2.0 TiB)

Number  Start (sector)    End (sector)  Size       Code  Name
# gdisk -l /dev/sdd
GPT fdisk (gdisk) version 0.8.10

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/sdd: 1565565872 sectors, 746.5 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): B8356612-A14C-4830-8CD8-871A26090A09
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 1565565838
Partitions will be aligned on 2048-sector boundaries
Total free space is 1565565805 sectors (746.5 GiB)

Number  Start (sector)    End (sector)  Size       Code  Name
#

QUESTION: How to make my external disk appear as one single device?

I run Ubuntu 2015.04 on Lenovo Thinkpad T520.

An Amazon review gives me hope that it is not a hard-coded limitation:

It did take some tinkering to format it as a single 3TB drive but as long as the majority require compatibility with Windows XP I don't blame Freecom. supportuk@freecom.com sent a speedy response to my request attaching a program to set the drive to a single 3TB partition. Sadly it is a windows program.

Maybe related:

• PCWorld article about why 3TB disks are often shown as 2.2TB (2^32*512)
• Similar-looking but old question with 1GB disk
• This Cyberciti article does not solve the problem, it is not about two devices

Answer 1

I ended up sending an email to Freecom, and they sent me a Windows executable called Freecom Mode Change Tool.exe. I asked for a Linux version but they told me:

Malheureusement non, le seul outil disponible fonctionne sur Windows uniquement.
[Unfortunately no, the only available tool works on Windows only.]

I had a hard time finding a Windows machine but when I did I executed the tool and was able to change it from "Split Mode" to "Standard Mode":

The disk now shows correctly as a single 3TB device:

Any Ubuntu-only solution would be very welcome!

Answer 2

The reason your disk showed up as a 2TB disk and a second, smaller, disk is that a lot of the (older) OSs out in the wild do not supports disks and partitions bigger than 2TB.

By "formatting" the device like this in the firmware, it appears to be two physical disks. By doing this, the manufacturer ensures that everyone can use the full size of the disk.

This Seagate article gives a bit more information about these "virtual" disks. Seagate also provides a Windows tool called DiskWizard to format the HDD as one big disk.

Instead of reformatting your disk, you can also use both disks as LVM partitions. They can then be used as one big disk. Create partitions smaller than 2 TB, and add them to a Logical Volume Manager (LVM) volume group, then create a logical LVM volume greater than 2 TB. Once the logical volume is created, you can format it with a file system of your choice.

This IBM article shows you one way of creating partitions bigger than 2TB on Ubuntu. Your kernel needs GPT support for that.

Answer 3

This is hardware. You can not turn it off (The review you cited suggests you can reflash firmware).
If you want to use it as a single disk, there are several ways in linux to combine several partitions into one. I recommend to set up BTRFS RAID 0. Instructions here. It will not incur noticable performance overhead. With BTRFS you can also turn on compression, which increases the read/write speed for external HDDs.