This method was tested with a SATA drive on a Proxmox VE 8.0.3 host and a Debian 12 VM.

Required preparations: A Proxmox VE host with a GNU/Linux VM, an unused drive attached to the server (can be USB, SATA, IDE, etc.)

Step 1: Navigate to the host you added the drive to.

Step 2: Navigate to "Disks". You should see the newly attached disk in the list.

Step 3: Wipe the disk. Please note that this will erase the data on it.

Step 4: Navigate to "Disks" ---> "Directory".

Step 5: Click on "Create: Directory".

Step 6: Step 5 will bring up a menu. There, choose the disk and select "ext4" as the filesystem. Here you can, and should give it a proper name. Also make sure that "Add Storage" is checked. Click "Create".

Step 7: Navigate to the "Hardware" tab of the VM you want to add the disk to. There, click on "Add", and on "Hard Disk" in the dropdown menu.

Step 8: At "Bus/Device", I chose SATA, because mine is a SATA disk.

Step 9: At "Storage", choose the drive you want to add.

Step 10: Adjust the disk size. You can check the right disk size at the left menu, where you should see your disk being added.

Step 11: Mount the disk in your VM. How to mount the disk?