Fixing a GPT partitioned NTFS formatted disk being inaccessible on Windows

partitioning

#1

I encountered a situation at work where a 3 TB external hard disk (USB) was partitioned using GNOME Disks using GPT as the partition layout and NTFS as file system.

2.1 TB worth of files were copied from another disk and everything seemed to be well. However… when plugged into a Windows computer, the partition layout looked a mess (and there was no drive letter so it wouldn’t have been possible to access the contents either!)

What happened?

It seems that Windows 10 didn’t recognise this disk as GPT and was reading it as MBR. This can be confirmed by opening Disk Management and seeing an unusual partition layout and some “unallocated space”. When plugged in Linux/Mac systems, it was reading correctly as GPT and accessing the files as expected.

Steps

It seems that GNOME Disks (in particular) creates a hybrid MBR, which confuses Windows. Instead, we just need to convert the MBR to being a “protective” one, we can use gdisk to do this. To the terminal:

You may need to install it first:

sudo apt install gdisk

Find out which is your hard disk by first running:

sudo fdisk -l

Spot which block device is the affected hard disk, e.g. /dev/sdc

Disk /dev/sda: 465.9 GiB, 500277790720 bytes, 977105060 sectors
Disk /dev/sdc: 250 GiB, 268435456000 bytes, 524288000 sectors

(Example condensed output)

Now start gdisk:

sudo gdisk /dev/sdc

The drive should current read along these lines:

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

Press these keys:

  • p to print the partitions, so you can double check this is the right disk.
  • x to enter the expert menu.
  • n to create a new protective MBR. This will overwrite the “hybrid” MBR.
  • w to write these changes to disk.

When you run gdisk again, you should see this:

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

Now this GPT drive can be used in Windows, Mac and Linux systems. :slight_smile:

:thumbsup: Big kudos to this answer!

This saves the need to wipe the drive and format it again, which would’ve been the worst case scenario.

Apparently this situation could also happen if the disk was formatted from macOS… so it may be a perk of formatting NTFS outside of a Windows environment.