Freeing space on your boot disk

The best space management is pre-emptive, and frees up storage before it’s needed, and you have to rely on macOS purging snapshots and cache files before the volume can accommodate an update or other important file. Rather than writing a huge file to try to force purging, plan ahead and create real free space in advance. Here are some suggestions.

Good housekeeping

Even the most methodical of us accumulates files that we don’t really need.

It used to be that finding duplicates was a rewarding activity, but that has become more complicated with APFS. Most copies and duplicates made on the same volume are now cloned, which means that APFS cunningly doesn’t initially create any new data, as both files share the same. When the two cease being faithful duplicates, though, changed data does start taking space, so perhaps we should now look for unwanted older versions rather than cloned duplicates. This also applies only to copies made on the same volume: even if they’re in the same container, copies on different volumes will take their full storage space. You’ll find fuller discussion of this here.


If you want to be systematic about this, then apps like DaisyDisk and GrandPerspective are far superior for discovering what’s taking up all that storage space than the built-in Storage feature. Some like to use commercial cleaning or housekeeping utilities, but I don’t recommend them because of all the problems they can cause. If anyone is going to trash files from my Mac, that’s going to be me, and not some well-meaning app with other ideas.

Move Documents

If your Documents folder is bursting at the seams, moving most if not all its contents to a different disk is a straightforward solution that has almost no adverse effects.

This has the slightly odd effect of changing their privacy protection. Documents stored in the Documents folder can only be changed by apps you approve to have access to that folder; move the documents to external storage and the same apps need a different privacy setting, so they have access to removable media.

You also need to use external storage that’s stable, not easily disconnected, and reliable, and ensure that all documents there are fully backed up to a different disk.

Move media libraries

Some of the largest collections of files in most Home folders are those containing media libraries, such as those for Photos and Music. Before Apple divided iTunes up, it was usually straightforward to relocate your music or movies libraries to external storage, but this has now become more difficult.

In my experience, Photos libraries remain the easiest to move elsewhere, and you can divide them up into multiple libraries if you wish. Keeping them in iCloud adds complexity, but in theory that should also enable you to reduce how much is kept locally. Remember that the only library you can share using iCloud Photos is your system Photos library: if you have other Photos libraries, you can access them locally, but can’t share them using iCloud.

Music is more complex than iTunes ever was, and normally has to store its libraries in the Music folder in your Home folder. However, you can move its media to external storage; since that’s what takes much of the space, this can offload much of their storage space, provided that you set it up carefully.

Apple’s Help and support documentation explains how to change the apps’ settings so that they can work with external libraries.

Avoid relocating Home folders

In the past, one powerful solution has been to relocate your entire Home folder to external storage. This used to be done by copying the whole Home folder to the external disk, then changing Advanced Options for that user in the Users & Groups preference pane, but that’s an option no longer available in System Settings.

This has become increasingly precarious since Catalina brought the Boot Volume Group, and growing expectations that your Home folder would be found on the Data volume. Unless you really know what you’re doing, can spend the time getting it right, and have plenty of backups, I wouldn’t recommend that you try this, at least not in Ventura. If you’re determined to try this, it should be more feasible with a second, standard user account than with the primary admin user. There are particular dangers in the latter when the external disk is disconnected or unavailable.

Compressing static files

If you can’t move files to a different disk, then you can try the traditional solution of compressing those you seldom need to access. It’s frustrating that macOS has long since done this transparently with system files, but as far as I know this isn’t readily available to third-party apps. Way back in the early 1990s, my Mac IIfx even had a hardware compression card in it to make this quicker and easier. Although our hardware no longer needs acceleration, it’s frustrating that macOS hasn’t yet caught up with features available twenty years ago.


On thinking more about this, I realise that transparent compression is of limited value for user files in APFS. Implementing compression and preserving the benefits of clone files and copy-on-write seems an impossible challenge. Apple primarily uses system-level compression for static files in macOS, where files are read-only and are only ever decompressed. Very few user files could remain read-only for long, and the rewards obtained by cloned files are far greater than could be achieved by compression.