I have a 128gb sandisk USB for my macbook pro 2015 13' (the storage capacity for the laptop is 128gb). Can I make the USB like my SSD for my mac (on laptop) so combined it will be 256gb total?
You could try making a DIY fusion drive, but I would expect bad results due to the slowness of the USB drive.
Worse - if you ever unplugged your USB drive or jolted it - the OS would likely crash. It would probably be better to just save less used files on the drive and mount it when needed.
