Adding a Mac partition to an external drive
I recently bought a 2 TB USB disk for backups, and without much planning proceeded to put disk images from a couple of Windows laptops on to the factory formatted NTFS partition. A few months later I decided I also wanted to backup my Mac to this disk, which is where the problems started. Firstly, in order to use Time Machine, I needed a HFS+ partition to back up to. Secondly, my Mac, running Sierra, won't write to NTFS, so I couldn't even do a manual backup to the existing partition. So I needed to shrink the NTFS partition and add a HFS+ one. My first stop was my Mac's Disk Utility, but it had its 'Partition' button greyed out with the tooltip "Disks with Master Boot Record partition maps can not [sic] be partitioned". Out of the frying pan My next thought was to use Linux to shrink the partition and convert the partition table to GPT, and then Disk Utility should be happy to add partitions to the disk. The shrinking and conversion was achieved smoothly ...