Intel Macs can be booted with Command-Option-R held to enter Recovery mode and be offered the latest available version of macOS which is compatible with that Mac. However, you’re limited as to which version of macOS this can install, and it will be downloaded in Recovery mode. If you want to install the same version of macOS as that provided in Recovery mode, you can now start up in Recovery and run the macOS installer there, selecting your external disk as the destination. Although macOS should cope with that, you’ll likely get confused. Encryption is up to you, although external disks don’t benefit from the hardware encryption provided to internal SSDs by T2 or M1 chips.Īvoid naming the volume Macintosh HD, which would normally coincide with your internal storage. If you prefer, and are sure that everything will cope, you can use APFS Case-Sensitive if you prefer. Normally, you should choose to format it in APFS but not Case-Sensitive, for greatest compatibility with software. You don’t and can’t do that on an M1 Mac: this only applies to Intel Macs with T2 chips.Īlthough you can do this immediately before you install macOS onto it, it’s usually better if you connect the external disk now, open Disk Utility, and format it ready for the installation. To do that, restart in Recovery mode (Command-R), open Startup Security Utility and enable your Mac to boot from external media. If you’re using an Intel Mac with a T2 chip, you first need to check that your Mac is configured so that it can boot from an external disk, unless of course you already know that because that’s what it’s doing now. As Apple doesn’t yet appear to provide complete instructions for the creation of a bootable external disk in recent versions of macOS, and the information which it does provide is at best misleading in places, this article attempts to remedy this for both Intel and M1 Macs.

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