Try these strategies to free storage on your Mac

For a while, computer storage was one of those issues that we no longer had to worry about. Hard disk sizes were rising and prices were falling, and if you found yourself low on free space, it was relatively easy to swap out the drive for one with far more capacity.

That was before SSD (solid state storage) disks became affordable enough to put into more machines. The performance benefits of SSDs are enormous, and if you’re toiling on an older Mac with a mechanical drive, replacing it with an SSD can be like getting a new computer.

Many of Apple’s products now are run on solid state storage, from all of its laptops to the Mac mini and the iMac Pro. The increase in speed, however, has resulted in a loss of storage, because although SSDs are far more affordable, they offer less capacity.

The MacBook Air, for instance, starts at a laughable 128 GB and goes up to 256 GB (slightly better), 512 GB (reasonable) or 1.5 TB (much better, although probably more than most people need), with increases in prices. Also, you have to commit to the storage when you purchase the machine, because the solid state memory is hard-wired to the logic board on some models.

Apple includes technology in macOS to compensate for low-storage situations, although it can make things confusing at times.

iCloud storage. If you have a fairly robust internet connection, you can store copies of files from the Desktop and Documents folders in iCloud storage. In System Preferences, go to the iCloud preference pane, click iCloud Drive, and enable the Desktop & Documents Folders option. Primarily, that makes it possible to access the contents of those folders on other Macs or iOS devices (using the Files app).

There’s also another option in macOS Sierra and later: Optimize Mac Storage. When that’s checked, macOS automatically deletes unused files from the local drive and leaves placeholders. If you need a document that has been removed, opening it first downloads the file from iCloud. The Photos app has a similar option for freeing up space occupied by photos. (Remember that you should also have a local backup of your data apart from iCloud.)

Ideally, you won’t notice that macOS is managing files on your behalf, and therefore you don’t need to spend the time handling it all manually.

Fudging storage numbers. That sort of under-the-hood file management applies at a deeper level under macOS High Sierra and macOS Mojave, which leads to odd free storage numbers.

To explain, let me give you a recent real-world example. Although I back up my iPhone to iCloud, I needed to make a separate local backup using iTunes. The iPhone contains about 150 GB of data, and when I looked at the status bar at the bottom of a Finder window, it reported around 300 GB of available space. (Go to View > Status Bar in the Finder to reveal the bar if it’s not visible.) However, iTunes reported there wasn’t enough free space to complete the backup.

The file system under macOS Mojave is APFS, a new way for the system, at its lowest level, to organize where and how bits are stored on disk. MacOS High Sierra also instituted APFS on Macs with SSDs; Mojave applied the file system to all drives, even mechanical ones. APFS is designed to more efficiently shuttle bits across the solid-state memory cells of SSDs, compared to the previous file system, Mac OS Extended.

That results in more efficient performance on SSDs, and also the ability to automatically store snapshots, which are representations of the disk’s state at a point in time. Think of APFS snapshots as Time Machine backups (in fact, at a low level the two are linked), which can allow you to roll back to a previous state in case something goes wrong.

MacOS automatically creates and deletes snapshots as needed, so older snapshots are considered purgeable. But iTunes, being iTunes I suppose, didn’t recognize that fact. That’s why the Finder reported plenty of free space, but I wasn’t able to make my backup.

There is a workaround, which involves manually deleting snapshots using the Terminal application to access the command line. Here’s how to do it:

1. Open Terminal.

2. At the text prompt, type “tmutil listlocalsnapshots /” (include the slash, but not the quotation marks) and press Return. That reveals any snapshots, which are named based on when they were made, such as “com.apple. TimeMachine. 2019-03-07-123320.”

3. Type “sudo tmutil deletelocalsnapshots 2019-03-07-123320” (substituting the oldest snapshot’s timestamp for the example one here) and press Return.

4. When prompted, enter the administrator password you use to log in to your Mac and press Return. You should see a response like, “Deleted local snapshot ‘2019-03-07-123320’.”

5. Repeat step 3 for any other snapshots you want to delete. Once you’ve entered your password, you don’t need to supply it for subsequent deletions.

After clearing out my old snapshots, I was able to free up enough space to make my local iPhone backup.

One other note about snapshots: When you run the First Aid feature of the Disk Utility application, it scans every snapshot in addition to the general state of the disk, which can take some time. If something is misbehaving on my Mac and I want to run First Aid, I’ll often delete all but one or two old snapshots to speed up the process.

There are plenty of other ways to clean up an overstuffed hard disk, but before you jump in and delete files manually, consider turning on the optimization options in macOS or check for numerous invisible snapshots. And if you’re not comfortable running commands in Terminal, look at utilities such as DaisyDisk or CleanMyMac for other options.

Jeff Carlson writes the Practical Mac column for Personal Technology and about technology in general for The Seattle Times and other publications. Send questions to carlsoncolumn@mac.com. More Practical Mac columns at st.news/practicalmac.