Macbook Air 2017 use an External SSD as a startup disk???

Hi there!

Using an external SSD as a startup disk on a portable Mac isn't always feasible. The external SSD would need to stay connected via. USB at all times, even when in sleep mode. This is why the external SSD solution is generally only recommended for desktop Mac computers.

This Apple Support article would be a good place to start: Free up storage space on your Mac - Apple Support.

-Jack

if you are running low on space, you can purchase an external HDD or SSD of sufficient capacity and move your larger files (videos, pictures, documents, etc...) to it. once they are on the EHD, you can simply erase the same files from your internal drive. and, if it's just going to be used for storage, you can use an HDD and save a few bucks over the cost of an SSD. FWIW, i personally keep very little on my internal drive.

additionally, you want to keep ~ 20% of your local drive as free space for proper operation of macOS.

My 2016 13" no touch MBP boots flawlessly from a standby external bootable SSD created by SuperDuper!. So do our other four Macs, years 2015 and 2020.

For the 2015 iMac, the speed boost with external boot was five fold: 90 MBps internal HHD read speed vs 450 MBps external SSD read speed.

I've never had the need to boot from an external drive, but a quick Google search revealed a good article on this: How to Boot a MacBook From External Drive

So apparently it's possible.

You can upgrade the SSD to a larger size fairly cheaply. Check OWC (Mac sales.com) for drives up to 2TB.