I would like to buy some more USB thumb-drives in order to make myself the following...
1.) Bootable USB w macOS Sierra
2.) Bootable USB w macOS High Sierra
3.) Bootable USB w macOS Mojave
What specs will I need in order to place one OS on each drive, and make it not only bootable, but functional (i.e. fast enough to be usable)?
I think I need to get USB 3, and am thinking I probably need 32 GB, but I don't keep up with consumer technology!
Thanks as always. 🙂
There's multiple possible methods for you to use.
Each of those macOS installers will fit on an 8GB flash drive. I have a small box filled with a couple dozen 8GB drives, with most setup as installer drives, every macOS system from Leopard to Mojave. As 8GB USB drives are getting harder to find now, 16GB for each is very usable. You could even make 3 partitions on a 32GB drive, and create bootable installers for each of the systems that you want, all on the same device.
The actual advertised USB speed (USB 2.0 or USB 3.0) is not terribly important, as long as the drive is bootable (test it after you make it). Some USB flash drives can be
really slow to write (you need patience waiting for some drives to finish copying files for this), but as long as they work (and boot your Mac), that's a usable installer. The
fastest installer set that I have is on an external enclosure (USB 3.1), with a small SSD. You can find decent (non-plastic) cases for less than $20, and cheap SSD (120GB for less than $20, or 240GB for less than $30), which can have multiple partitions. The one that I use has partitions for Leopard to Mojave installers, and enough space left to make backups of (small) customer drives. The copy process for any installer completes within 2 or 3 minutes, then you are subject to whatever the write speed is on the Mac's boot drive (the installer app is done at that point). The external SSD that I described is what I recommend for that.... but I also have individual installers on flash drives. I do use both.
finally - I bought a 64GB USB flash drive for about $15 last December. That one also has a multiple partition setup with the systems that I most commonly install: Lion, Yosemite, El Capitan, High Sierra, and Mojave. Works great, and is in my pocket most days