How to free up ‘System Data’ and other storage on your Mac
TL;DR:
Most of the time, the data taking up space on your drive are your own data. If you need to free up space, the best approach is to move some of your data to an external drive or cloud storage. Do NOT install apps that purport to ‘clean’ or ‘optimize’ your Mac, in most cases they do far more harm than good.
The abridged version:
One approach to free up space is to use Apple’s automatic options to Optimize storage space on your Mac. If you want to manage things yourself or need to free up more space than Apple’s approach accomplishes, you need to find and remove (delete or copy to external storage) sufficient data to free up the space you need. In addition to the obvious categories like photos, applications, downloaded movies and music, etc., you may find that some of those categories are unexpectedly large and/or that ‘System Data’ is taking a significant amount of space.
Much of what macOS puts in that category are data stored in the hidden Library folders by various applications, one example is Microsoft Outlook email attachments. You can navigate to your Library folder in Finder by holding the Option key and clicking the Go menu, then selecting Library. If folder sizes aren’t showing, press Command-J and tick the box to Calculate all sizes. You can sort by size and explore the largest folders and subfolders first. You can also use a 3rd party disk inventory tool like OmniDiskSweeper (free), Disk Inventory X (free) or DaisyDisk (paid) to get a graphical and/or heirarchical view of your largest files/file types including those in the Library folders. Note that some folders/files in your Library folder may also be hidden. Command-Shift-. (period) will globally toggle viewing of hidden files on and off. The 3rd party tools will show hidden files (they will appear with a period at the beginning of the filename, (e.g., .Caches).
Obviously, don’t arbitrarily delete things if you don’t know their function, but there’s a good chance you’ll find actionable items. On my systems, I see support files for applications I’ve previously deleted, cache files for messaging apps that I probably don’t need, etc. Files stored by apps like Outlook should be deleted from within the app itself. To reiterate the warning, there will also be files in there that you don’t recognize but are important. Google can be your friend here but look for primary sources not just the AI summaries.
The full version:
Modern Macs are generally as compact as possible, and for many years the internal storage in most Macs has comprised one or more SSDs integrated directly into the main logic board. As a result, it is not possible to ‘upgrade’ the internal storage of a modern Mac (the Mac Pro is the sole exception). The amount of storage you select when you purchase the Mac is the amount of internal storage that you will have available until you get a new Mac. Keep that in mind when you buy your next one (meaning, if you’re reading this tip then you should probably more storage next time you upgrade your Mac).
Parkinson’s Law can be generalized to suggest demand always expands to match supply. In terms of your computer’s internal storage, that means at some point, no matter how much available internal storage you selected when you bought your Mac, eventually you may find that your drive is getting full and you need to free up space. In general, you should have at least 10% and ideally around 20% free space on your Mac. That space is needed for your Mac to function optimally, including periodically to download macOS updates before they can be installed.
Apple’s advice on freeing up storage space on your Mac is here: Free up storage space on Mac. You can consider using Apple’s ‘one-click’ options accessed via System Settings > General > Storage, including Store in iCloud that stores your Desktop and Documents folders in iCloud (if you have enough space there) and keeps only recently accessed files on your Mac, Optimize Storage that removes previously watched Apple TV content and older Mail attachments, and Empty Trash automatically.
Personally, I prefer more control over my files and would rather avoid letting Apple make those decisions for me. If what is taking up you space is mostly photos, downloaded movies and music, etc., then freeing up storage may be as simple as deleting them or moving them to external storage. If you’re reading this tip, then it’s probably not that simple and one reason for the length of this tip is that what is taking up your storage space depends heavily on what you have installed on your Mac. There isn’t a one-size-fits-all solution.
The first thing to know is that most of the time, the data taking up space on your drive is your own data. There are some instances when macOS will (appropriately or inappropriately) generate data that takes up space, those will be discussed below. What this means in practice is that you will most likely need to make choices about what data you want to keep on your internal drive and what data you want to store on an external drive. But first, you need to figure out what is taking up your space.
For this User Tip, I’ll use examples from two Mac notebooks, a 16” M4 Pro MacBook Pro with 2 TB of internal storage running macOS 26 Tahoe, and a 16” M1 Pro MacBook Pro with 1 TB of internal storage running macOS 15 Sequoia.
The first stop for most people when looking to free up space is the graphical and tabular display of your data shown in System Settings > General > Storage. On the M4 Pro MBP, it shows the following:
The different color bands are categories to which your Mac assigns the files, including Apps, Photos, Documents, etc., with gray bands used for ‘system’ items such as System (macOS files), Trash, and System Data. The categorization is driven by Spotlight, so one thing that may help at the outset is to Rebuild the Spotlight Index. In some cases, System Data shows ‘Calculating…’ and never seems to finish. Rebuilding the index can correct that situation, as well.
I would consider this Mac to be ‘well behaved’ in that I don’t see any big surprises on the settings pane. The biggies category is Documents (something of a catchall), but clicking on the (i) to the right shows the largest portion is my 151 GB iMovie Library. Photography is a personal hobby, and I keep the last 5 years of RAW images locally (thousands of files) and those are classified as documents by macOS. Photos is the second largest category at 201 GB, and that’s the size of my Photos Library so all good. Applications is the first sign of a small discrepancy. The additional info shows some good-sized apps like Topaz Photo AI at 15 GB and multiple Adobe apps, but Get Info on the Applications folder shows that it’s only 63 GB, so what about the ‘missing’ 18 GB?
In this case, that discrepancy is due mainly to Adobe apps, for which some in the Applications folder are merely aliases to the actual application file that is stored in the system-level Library folder, and macOS correctly includes those additional apps in the total. Additional files in Application Support are also included in the applications category. System Data is a reasonable 31 GB on this Mac.
On the M1 Pro MBP, it shows the following:
In this case, the obvious choice to free up space would be the 141 GB of movies in the TV category (they were downloaded from Apple TV and stored locally for entertainment on long flights). On this Mac, the Applications category jumps out as being quite large at 284 GB, especially when Get Info on the Applications folder shows only 40 GB.
In this case, most of that is due to a 200 GB local cache for my work cloud storage service, in this case stored the Application Support folder in my user Library. They are data files (PowerPoint, Word, etc.) but stored in a hidden cache folder so macOS counts them with Applications.
On this Mac, System Data is taking up 70 GB. On some Macs, it takes up much more. So, what is in the vaguely-named System Data category? Essentially, it’s a catch-all category for files on the Mac that are not categorized as something specific like Apps, Documents, TV, etc. For the most part, these files are created and saved by various apps on the Mac, mainly in the ~/Library folder. That’s why there isn’t a one-size-fits-all solution, because it will depend on what apps you have installed.
For example, in the case of the M1 MBP, of the 70 GB of System Data, about half of that is Microsoft Outlook email attachments (these are mainly images and PDFs that display inline), buried several levels deep in the ~/Library folder.
There are several ways you can go about identifying what is taking up space in the ~/Library folder.
One is manually – you can navigate to your Library folder in Finder by holding the Option key and clicking the Go menu, then selecting Library. If folder sizes aren’t showing, press Command-J and tick the box to Calculate all sizes. You can sort by size and tackle the largest folders and subfolders first. Note that some folders/files in your Library folder may also be hidden. Command-Shift-. (the period key) will globally toggle viewing of hidden files on and off. The 3rd party tools will show hidden files (they will appear with a period at the beginning of the filename, (e.g., .Caches).
It’s often easier to use a 3rd party disk inventory tool like Disk Inventory X (free), OmniDiskSweeper (free), or DaisyDisk(paid) to get a graphical and/or hierarchical view of your largest files/file types including those in the Library folders. These apps do not distinguish what is in System Data, but they will show everything taking up space on your drive and allow you to sort it by size and to find it, regardless of whether About this Mac > General > Storage puts it in a specific category or in System Data. Note that for all of these apps, you’ll be prompted to grant access to various portions of your system (Downloads, iCloud, OneDrive, Music, etc.). These examples are from my M4 Pro MBP.
DaisyDisk is organized based on location in the file system of the drive, showing the sizes of hierarchical folders and allowing you to drill down into them (the same as you could do manually, but the app graphically highlights the largest folders). DaisyDisk is available on the Mac app store, but that version does not allow full disk scanning, so for purposes of finding large, hidden files you are better off purchasing it from the developer’s website linked above.
‘Hidden space’ comprises other volumes on the Mac (RecoveryOS, for example) and APFS snapshots (more on that later).
Personally, for this use case I prefer Disk Inventory X because it is organized based on file type and not file location. Note that this is a very old app, and it is not signed by Apple meaning that after trying to launch it and not being allowed to do so, you’ll need to open System Settings > Privacy & Security > Security section and give the app permission to run anyway. I completely understand that some people will not be comfortable doing so.
For example, you can click on a color block and see the associated file type (red arrow), in this case Canon RAW images. You can click on a block and see the file location (red arrow), or you can drill down in the folder hierarchy that is sorted by size. The grouping by file type made it easy to find out that Outlook was using 56 GB of data on an older Mac.
OmniDiskSweeper does not offer a graphical interface, but does provide an easy way to browse all your data hierarchically sorted and color-coded by size.
So…now that you’ve hopefully identified the big files and collections of small files taking up large chunks of space on your drive, the next question is what do you do with them? The answer is that it depends on the files and their source. Obviously, don’t arbitrarily delete things if you don’t know their function – there’s a reason that the ~/Library folder is hidden by macOS. However, there’s a good chance you’ll find actionable items. On my systems, I see support files for applications I’ve previously deleted, cache files for messaging apps that I probably don’t need, etc. Files stored by apps like Outlook should be deleted from within the app itself. To reiterate the warning, there will also be files in there that you don’t recognize but are important. Google can be your friend here but look for primary sources not just the AI summaries.
Once you’ve started freeing up space, the next question is how much free space do you need? The absolute minimum is ~20-25 GB free space, and as a rule of thumb you should aim to have 15-20% of your total internal storage as free space. Terminology is important here – free space is not the same thing as available space. The one that matters is Free space, but what macOS shows in most places is Available space. Available space includes both free space and ‘purgeable’ space, the latter comprises system caches, snapshots and other data that macOS can delete if it decides more free space is needed. However, there is no way the user can force those data to be purged.
The place to check how much Free space you have is in Disk Utility (in Applications > Utilities), by selecting the main container disk below the drive itself (you may need to select View menu > Show all devices to see it). For example, on my M4 MacBook Pro, the Storage settings pane and Get Info on the internal drive show 1.24 TB of Available space, whereas Disk Utility shows there is 1.15 TB of actual Free space, 90 GB less than ‘available’.
Note that you can also see the Free space in the System Report (System Settings > General > About > System Report button, at the bottom > Storage).
One more topic that frequently comes up in this context are local snapshots made by Time Machine. If you are using Time Machine to back up your Mac (if not, you should definitely do so unless you’re using another backup method), then it will create and store hourly snapshots on your internal drive for the past 24 hours plus the last successful backup if older than that. You can view snapshots in Disk Utility – select the top-level volume of your internal drive (Macintosh HD unless you’ve renamed it, as I have), then View menu > Show APFS Snapshots (some explanations of the information shown can be found at this link). Personally, I have a local NAS as my primary backup and a pair of 4 TB SSDs as secondary backups that I swap offsite every week. You can see that my Mac has stored 24 hours of snapshots, plus one from 3 days ago and one from 10 days ago (the two completed backups to the SSDs).
Deleting all of those snapshots would free up 50 GB of space (the private size at the bottom is the one that matters, not the sum of the individual snapshot sizes). However, that’s a short-lived solution at best since Time Machine will simply recreate them. Still, this could be a useful step if the goal was to temporarily free up space, to perform a macOS update, for example.
If all else fails and there’s no other way you can free up sufficient space, there remains the ‘nuclear option’ – make a fresh Time Machine backup, erase your Mac, then transfer only your user account(s) in Setup Assistant and reinstall only the necessary apps.
Hopefully you are able to free up sufficient space to keep your Mac running smoothly.
(This tip is an expanded and updated version of an earlier tip, What is “Other” storage on a Mac, and how can I clean it out?)