Change MBR to GPT on external hard drive with data:
I found a way for the internal one here. However the External drive is a Data drive only, I dont't need to care about any bootloaders etc. So is there an easy way to do it? It is a 3TB external drive, the setup in Gpartet looks like that:
| 8MB unallocated space|1,36TB ntfs with ca 300GB of data|1,36 of unallocated space|
If this is a data drive only, I believe the start/end margins are sufficient, and a simple
sudo gdisk /dev/sdX
(follow steps) should do the job, converting the MBR to a GPT.