Usually connecting external disks in Linux is easy. Plug it in, run fdisk -l or lsblk | grep disk to identify the device ID, and then mount it.
Unfortunately in this instance, plugging in my Seagate 2TB wasn’t so simple. The server is running Proxmox:
# uname -a Linux proxmox01 4.4.6-1-pve #1 SMP Thu Apr 21 11:25:40 CEST 2016 x86_64 GNU/Linux No device showed up on lsblk or fdisk -l.