How to Partition an External Hard Drive for macOS
TL;DR macOS expects 200 MB EFI System partition in the beginning of a hard drive, don't like unformatted partitions and creates 128 MB Apple boot partitions after each real partition whenever you format it.
I needed to partition an external hard drive to be usable on macOS (for Time Machine backups). I've partitioned the drive using GPT scheme and created one unformatted Apple HFS/HFS+ partition on Arch Linux using fdisk. It was not recognized (the inserted disk is not readable dialogue), nor was I able to format the partition (with "Media kit reports not enough space on device" error) which was shown as full in the Disk Utility. When I have formatted the partition (using mkfs.hfsplus from hfsprogs) the partition was recognized but I was unable to initialize it for Time Machine or format with the same error as before. Finally I have partitioned the drive from macOS and created a new partition. Looking at the drive with fdisk I've discovered that EFI System partition was created in the beginning of the disk with size of 200MB. When I have recreated the same partitioning layout using fdisk it was recognized properly. After setting up Time Machine backups on the created partition I have inspected the disk once more. The partition type was changed to Apple core storage and a 128 MB partition was created after it. When I created another partition for the second MacBook I got one more 125 MB Apple boot partition. The resulting partition table was:
Device Start End Sectors Size Type /dev/sdb1 2048 411647 409600 200M EFI System /dev/sdb2 411648 268847103 268435456 128G Apple Core storage /dev/sdb3 268847104 269109247 262144 128M Apple boot /dev/sdb4 269109248 478824447 209715200 100G Apple Core storage /dev/sdb5 478824448 479086591 262144 128M Apple boot
So 5 partitions instead of 2 I actually needed. Here Apple's partitioning policy can be found describing when additional partitions are created with some justifications trying to answer why they are needed.