Most new Macs do not have expandable storage—it’s part of the computer, so it’s important to buy more than you think you might need when you purchase it.

However, many recent Macs have removable storage modules that can be exchanged for higher-capacity ones. You can see what model of Mac you have under Apple Menu > About This Mac, and how much total storage you have under the Storage tab.

Upgradeable Macs are:

• all 21.5″ iMacs, including the current model
• 27″ iMac through 2019
• two-port MacBook Pro from 2016 and 2017
• MacBook Pro through 2015
• MacBook Air through 2017
• Mac mini through 2014
• all Mac Pro models

Most of these machines require an Apple-specific module, and they vary by machine and year, so it can be a tricky thing to figure out what you need to get. You also need, if you don’t like taking apart computers, someone who can perform the installation for you. If you’re replacing a 2.5″ drive (like a hard drive, or an SSD in older iMacs and MacBook Pro with an optical drive), then you can buy a 2.5″ SSD from any vendor, like a Samsung EVO. More likely, you have to get an Apple-specific SSD module. For those, you have the following options for what to purchase, in order of expense:

• an original Apple part (most compatible; usually previously used since they came from inside a computer; can be purchased from eBay, Amazon, and Mac parts vendors like Beetstech)
• a vendor-supported, third-party module designed for Macs (the best known of these are from Other World Computing)
• a vendor-supported, commonly available m.2 SSD module with with an adapter (Fledgling makes these)
• bring your own commonly available m.2 SSD module and adapter; no one will support you

The problem with all the non-Apple offerings is that they may cause problems with your Mac waking up from sleep; if this is the case, then you have to disable the computer’s ability to “hibernate,” aka “deep sleep,” when it drains all the way down; instead it will suddenly turn off completely when the battery completely drains, with no attempt to shut down cleanly or preserve whatever you were doing. Also, while it’s unlikely, Apple may update your Mac’s firmware during an ordinary OS update or upgrade, and since compatibility with third-party vendor hardware is not a high priority for them, the update may be render the module you were using incompatible. It has happened before, and vendors have had to scramble to figure out how to update their previous SSD modules.

This is just the overview; the hard part is figuring out what to get and who’s going to put it in (if it’s not you). I may try to make another post with what module I recommend for what machine.

Thanks to this incredible article at Beetstech for detailing all of the myriad different proprietary SSD’s Apple has used. If you’re technically inclined, it’s a very interesting read, and they also sell the original Apple modules right from the site, if that’s the direction in which you wish to go.