If you’re using Time Machine, the built-in backup program on the Mac, you should know that you can save space on your Time Capsule or external drive by excluding stuff that you don’t need to have backed up. (And if you’re not using Time Machine or another backup program at all, then I know what should be number one on your to-do list today.)
The way to do this is simple, but before you jump headlong into excluding your Pictures folder (who would need THAT backed up?!) or, say, your applications, know that I really, truly don’t recommend doing this for most of your files. If space is not a crucial concern, it’s better to just back up everything you’ve got, especially since Murphy’s Law says that the minute you exclude a folder, you’ll accidentally save a crucial file there. Right before your hard drive fails. And your house catches on fire.
If you do have items you’d like to exclude, though—for example, if you’ve got a ton of iTunes movies that you’re comfortable re-downloading from Apple if necessary—then here’s what you’ll do. First, visit System Preferences > Time Machine by either clicking on the Apple Menu in the upper-left corner of your screen or by choosing it from the Time Machine menu bar icon.
Once you’re there, click on “Options” in the lower-right.
Within that dialog box, you can click the plus button to add a new exclusion.
As you can see, this box is also handy if you’d like to ask your Mac to continue backing up when it’s not plugged in or if you want to be notified when old backups are deleted. Additionally, this is where you’ll go if you need to un-exclude something. If you’ve got an external drive that contains your Photos library or other important data, it would be an excellent idea to come here and remove it from the exclusions list so that it can be backed up, too.
Anyway, you’ll choose the files or folders to exclude from your backups after you’ve clicked that plus button…
…and when you’re finished, you’ll soon be able to see the size of your excluded items and the amount of space your whole backup will consume.
See how I’ve excluded the Pictures folder? That’s for instructional purposes only. Please don’t actually do that unless you hate your family and want to see every image you’ve ever taken of them disappear.
You can then continue clicking the plus button to add more files or folders to the exclusions list, but when you’re finished, click “Save,” and your backups will be smaller! Neat! While I’ve got your attention, though, this is a good time to mention that I strongly encourage you to have at least one on-site backup and one off-site backup. I’ve been using CrashPlan as my own off-site solution for years, and I love it, but you do whatever makes you happy. As long as what makes you happy is multiple redundant backups, that is.