When trying to partition a flash drive using the Disk Utility GUI, sometimes you’ll run into the issue where the Partition button is greyed out. This is usually due to the flash drive having Master Boot Record(MBR) partition maps for PC compatibility… but unfortunately this also means it’s less user-friendly to partition. Fortunately for us, we’ve got terminal and the diskutil cli so let’s get started.
First, open terminal and identify which disk is the flash drive that you want to partition:
For me, the desired disk was /dev/disk2 so let’s erase it and set the new partition map as GPT:
diskutil erasedisk hfs+ External GPT /dev/disk2
And that’s it, you can now partition your flash drive.