Unmount all the volumes on the disk using: diskutil unmountDisk disk2 The free space is indicated by this line (the numbers are 512-byte sectors, so just under 100GB free space: 409640 195575768Īpple requires 128MiB (262144 sectors) free space following a partition, so the new partition can be 195575768-262144=195313624 sectors. Your GPT looks like this: start size index contents OK, your partition tables look fine (a valid GPT and a correct protective MBR), so I don't know why Disk Utility is failing you in this instance, but you should be able to create a partition in the empty space using the gpt command-line utility. Read through the whole instructions before doing anything to make sure you understand all the steps.) that said, the changes here are not particularly dangerous. (Before proceeding, please make sure the disk in question is still disk2, you have backups of your data, etc.

Is there a way to accomplish this with diskutil? I’ve only found ways to change (or erase, or split etc.) existing partitions by e.g.

I'd like to reclaim that space, but Disk Utility doesn't let me create a new partition there (it just does nothing when I click 'Apply'). I have deleted the first partition on my external HD such that it now has 100GB of free space at the beginning of the partition.

Diskutil delete partition