Why Is System Data So Large on Mac?

System Data is the leftover category

On macOS Ventura 13 and later, open the Apple menu, choose System Settings, click General, then click Storage. On earlier macOS, the same categories are under About This Mac, then Storage. Apple’s July 6, 2026 storage article says this view shows how much space each category of files uses, and that it updates as you free space.

System Data, also labeled Other on some versions, is the general category. It measures Apple and third-party files that do not belong to a more specific category such as Applications, Documents, or Trash. Apple’s System Information guide, whose version list runs from High Sierra through Monterey, gives the concrete examples: log files, caches, VM files, other runtime system resources, temporary files, fonts, app support files, and plug-ins. You cannot manage the category itself. macOS manages it, and the size changes with the current state of the Mac. You manage the underlying files in Finder, or in the app that created them.

That is why a developer Mac often shows a huge System Data number. Many caches, logs, and support files have no category of their own, so they are counted there instead of under Applications or Documents. Cleaning those folders is a different job from deleting “System Data.” The developer disk-space guide and the cleanup checklist cover the regenerable caches. This page is about the number itself, and about Time Machine local snapshots.

Why the numbers do not match

Finder Get Info, About This Mac, and System Settings are not three views of one folder.

Adding up the folders you can see in Finder will not equal System Data. The category is system-wide, it excludes files that already landed in another category, and it changes while macOS is measuring. Free space and available space are also different: available space includes purgeable disk caches. A sparse compiler cache is a separate case where Finder’s logical size is larger than the blocks actually allocated.

Local snapshots count as available space

Time Machine keeps some backups on the Mac when the backup disk is not connected. Those are local snapshots. Apple’s July 6, 2026 snapshot article says Time Machine saves one snapshot of the startup disk about every hour and keeps it for 24 hours, keeps an additional snapshot of the last successful Time Machine backup until space is needed, and on macOS High Sierra 10.13 or later saves another snapshot before a macOS update.

The Mac counts snapshot space as available storage. Snapshots do not consume the space needed to download, copy, or install. Time Machine stores them only on disks that have plenty of free space, and it deletes them as they age or as other work needs the space. A large System Data figure plus a comfortable “available” number can both be true while snapshots are still there.

Let Time Machine delete snapshots

Apple’s documented way to delete local snapshots by hand is to turn off automatic backups, wait, then turn them back on. Time Machine remembers the backup disks it was using.

• Open Time Machine settings from the Time Machine menu, or in Ventura 13 and later choose System Settings, General, Time Machine.
• In Ventura 13 and later, click Options, choose Manually from Backup Frequency, then click Done. On Monterey 12 and earlier, deselect Back Up Automatically, or use the Off/On switch if that is what you see.
• Wait a few minutes so the local snapshots can be deleted, then turn automatic backups on again.

Do this before reaching for a delete command. The snapshots are local restore points, including the copy of your last successful backup and, on High Sierra and later, the snapshot taken before a macOS update.

Thin or delete one snapshot date

tmutil can list, thin, or delete local snapshots. These are the three commands. Replace the placeholders. Do not pass / to the delete command.

tmutil listlocalsnapshots /
tmutil thinlocalsnapshots / <bytes> <urgency>
tmutil deletelocalsnapshots <date>

tmutil listlocalsnapshots / lists local snapshots of the startup volume. The manual’s example of a local snapshot name is com.apple.TimeMachine.2011-07-03-123456.local. To print the dates alone:

tmutil listlocalsnapshotdates /

Dates use YYYY-MM-DD-HHMMSS.

tmutil thinlocalsnapshots / <bytes> <urgency> asks Time Machine to thin snapshots on /. The byte count and the urgency are optional. When you pass both, tmutil attempts, at an urgency from 1 to 4, to reclaim that many bytes. If you omit urgency, it uses its default. The manual does not say which end of 1 to 4 is more aggressive, and an attempt is not a promise that the bytes come back as free space. This example uses urgency 1 only because 1 is inside that range, and two billion bytes only as a modest starting amount:

tmutil thinlocalsnapshots / 2000000000 1

List the snapshots again after it finishes. If you still need the space, raise the byte count and try again. Leave the backup disk’s copies alone.

tmutil deletelocalsnapshots 2011-07-03-123456

The date above is the manual’s example of the timestamp format. Substitute one of your own dates. Deleting that snapshot removes a local restore point. If you still need those versions, confirm the backup disk has them first.

The tmutil manual says several, but not all, verbs require root and Full Disk Access. The entries for these list, thin, and delete verbs do not say they require root. Run the commands as written above. If Terminal cannot read Time Machine data, grant it Full Disk Access. On Ventura and later that control is in System Settings, Privacy & Security, Full Disk Access. The manual, dated 10 June 2015, still points at the Privacy tab of the older Security & Privacy pane.

What DevCleaner does

DevCleaner does not list, thin, or delete Time Machine local snapshots, and it does not run tmutil. The confirm-clean sheet and the deletion record say that free space may not rise right away, and they name Trash, Time Machine local snapshots, and APFS purgeable space. After a clean with no failures, the dashboard footer shows a shorter version of that note. The menu bar can show it briefly too.

FAQ

What is System Data on a Mac?

It is the remainder. Apple’s current storage article calls System Data, or Other, the space used by Apple and third-party files that do not belong to a more specific category. Apple’s System Information guide adds examples: logs, caches, VM files, other runtime resources, temporary files, fonts, app support files, and plug-ins. macOS manages that category, and its size changes with the state of the Mac.

Why doesn’t System Data match Finder or About This Mac?

They measure different things. System Settings Storage, and About This Mac Storage on older macOS, is a category total. Finder Get Info measures the folder you selected. Free storage is physically open space. Available storage also includes purgeable disk caches, and the same space can be both available and used. Time Machine counts local snapshot space as available storage.

Will thinlocalsnapshots free the exact number of bytes I pass?

No. When you pass a byte count and an urgency from 1 to 4, tmutil attempts to reclaim that many bytes by thinning snapshots. The manual does not promise the space returns, and it does not say which end of 1 to 4 is more aggressive. List the snapshots again afterward.

What happens if I pass / to deletelocalsnapshots?

A mount point deletes every local snapshot on that disk. A date in the form YYYY-MM-DD-HHMMSS deletes every local snapshot with that timestamp on every mounted disk. Pass one date from tmutil listlocalsnapshotdates when you mean one timestamp.

References and scope

Reviewed on October 12, 2026 against DevCleaner 1.15.0, Apple’s support articles published July 6, 2026, the System Information storage guide, and the tmutil(8) manual dated 10 June 2015. Storage labels and settings paths change between macOS versions. The commands are inspection and deliberate snapshot actions, not a promise of how many gigabytes your Mac will recover.

• Free up storage space on Mac
• See used and available storage space
• About Time Machine local snapshots
• tmutil(8) manual