The installer drive must be formatted as a Mac OS Extended (Journaled) volume with a GUID Partition Table.
To create a bootable High Sierra or Sierra installer drive, you just need the appropriate aforementioned installer and a Mac-formatted drive (a hard drive, solid-state drive, thumb drive, or USB stick) that’s big enough to hold the installer and all its data-an 8GB thumb drive is perfect. (Developers can get the current release version of High Sierra through the developer download site-scroll down to “Release Software.”) What you need
You can get the latest version of the High Sierra or Sierra installer from the Mac App store. How do I get the High Sierra or Sierra installer? 2 Here’s this year’s version, for both macOS High Sierra (10.13) and macOS Sierra (10.12), of my annual how-to guide. 1 It’s great for installing the OS on multiple Macs, because you don’t have to download the ~5GB installer onto each computer, and it serves as a handy emergency disk if your Mac is experiencing problems. I’ve long recommended creating a bootable installer drive-on an external hard drive, thumb drive, or USB stick-for the version of macOS you’re running on your Mac.
