Guide · Mac

Time Machine probably isn't backing up your external drive

If your photos or footage live on an external SSD, the way most people edit from one, Time Machine is likely leaving that drive out. Here's how to check, and how to back that drive up to another one.

Check

Time Machine backs up your Mac, and leaves external drives out unless you tell it otherwise. On a Mac with Time Machine set up, both external drives connected to it were on its list of things not to back up.

To see it for yourself, plug in your work drive, open System Settings > General > Time Machine and click Options. If your work drive is listed under Exclude from Backups, nothing on it is in your Time Machine backup.

Two ways to fix it

Add the drive to Time Machine. Select it in that list and click the − button under it. Time Machine then backs it up whenever the work drive is connected during a backup. That works if your Time Machine drive has room for your Mac and your work together.

Copy the work drive to a second drive of its own. Better when the work drive is big, when it travels without your Mac, or when you want a copy that's just your project folders, in the same layout, that you can plug into any computer and open.

The rest of this guide sets up the second way, with Stow™.

Back up the work drive to another drive

1. Plug in both drives and open Stow. Click New sync.
2. Under From, choose the folder your work is in on the work drive. Under To, choose a folder on the backup drive. Choose folders, not the drives themselves: a drive also holds macOS's own hidden files, which can't be copied.
3. Choose Only ever add, so clearing old projects off the work drive to make room never removes them from the backup.
4. Under When should it run?, choose Whenever the drive is plugged in. Plug the backup drive in when you're done for the day and it runs.
5. Read the sentence at the bottom, then click Save and preview results. Stow shows every file it's about to copy before anything moves. Click to run it.

The first run copies everything, so give it time. After that each run copies only what's new or changed. When Stow's menu bar item says Everything up to date, eject the drive.

Edited files replace their older copy on the backup, and the older copy is kept for 30 days in a safety net on that drive. If a run can't finish, Stow says so and why.

Keep Time Machine too

Time Machine is still the right backup for your Mac itself: your apps, settings, and anything you keep on the internal disk. This adds the drive it leaves out.