For storage questions, Disk Utility shows what Finder and Storage settings leave out: how each disk is divided into containers and volumes, how much each volume uses, and how much is free or purgeable. It also lists APFS snapshots, checks a disk for damage with First Aid, and adds, erases and partitions volumes.
Most storage questions need only three things in it. Choose View › Show All Devices to see the whole layout. Select a volume to read its Used, Other Volumes and Free bar. Click Info in the toolbar for the available space split into free and purgeable.
The rest is for specific jobs. View › Show APFS Snapshots lists the snapshots that hold space no folder shows. First Aid repairs a damaged file system. Add Volume, Erase and Partition change the layout, and the last two erase data, so they come with warnings below.
Disk Utility doesn't tell you which files are large or what they are. For that you need Finder, Storage settings or a disk analyzer. It tells you where the space is at the level of disks, which is often the missing half of the answer.
Opening Disk Utility and reading its window
Everything here follows Apple's Disk Utility guide for macOS 27 Golden Gate and the menus of Disk Utility on macOS 27.
How do you open Disk Utility?
In Finder, choose Go › Utilities and double-click Disk Utility; it lives in /. You can also search for it with Spotlight, or find it among your apps in the Dock.
Apple also offers it in macOS Recovery, from the Recovery app's window. Use that copy to repair or erase your startup disk, because macOS can't change the disk it's running from.
Why does the sidebar show so few disks?
Because the first time you open it, Disk Utility uses Show Only Volumes, which Apple describes as listing just the volumes on each device. That hides the containers and the physical disks they belong to.
Choose View › Show All Devices to see the full structure. Apple says some tasks, such as erasing a whole storage device, are possible only in this view. It's the better view for any storage question.
What are devices, containers and volumes?
- A device is the physical disk, or a disk image macOS treats as one. It sits at the top of each group in the sidebar.
- A container is a partition formatted as APFS. Its volumes share its free space.
- A volume is what you see in Finder, with its own name and files.
A disk formatted as exFAT or Mac OS Extended has no container: each partition holds one volume with a fixed size. That's why the container idea only matters for APFS disks.
What do the toolbar buttons and menus do?
| Control | What it does | Can you undo it? |
|---|---|---|
| Info | Opens details about the selected item | Nothing to undo |
| First Aid | Checks and repairs the file system | Nothing to undo |
| Add Volume | Adds an APFS volume to a container | Delete the volume again |
| Delete Volume | Removes a volume and its data | No |
| Erase | Erases a volume or a whole device | No |
| Partition | Divides a disk into containers | Not without erasing |
| Restore | Copies one volume over another | No; the destination is erased |
| Mount and Unmount | Makes a volume available or not | Yes |
The View menu holds Show All Devices, Show Only Volumes and Show APFS Snapshots. The Images menu holds the disk image tools: Convert, Resize and Scan Image For Restore.
What do Mount, Unmount and Eject do?
Unmount makes a volume unavailable to Finder and apps while the disk stays connected; Mount brings it back. Eject disconnects the whole device so you can unplug it. None of them changes what's stored, and an unmounted volume still takes its space on the disk.
The volumes on your Mac's startup disk
Select your Mac's internal disk with all devices showing, and you'll find more volumes than Finder ever shows. That's normal, and none of them needs your attention for storage.
Why are there two Macintosh HD volumes?
Apple's guide says macOS is installed on a volume group of two volumes: a system volume, Macintosh HD, and a data volume, Macintosh HD - Data. The system volume holds macOS itself; the data volume holds your files, apps and settings.
Finder shows them as one. In Disk Utility you see both, with the data volume holding nearly everything. The post on Macintosh HD and its Data volume explains the split in detail.
What are Preboot, Recovery and VM?
They're support volumes in the same container. Preboot holds what your Mac needs to start up, Recovery holds macOS Recovery, and VM holds virtual memory files, the swap that macOS writes when memory runs short. Disk Utility shows them only with all devices showing.
Their sizes vary. Here they are on one Mac, measured while writing this post:
- Data, your files and apps421.4 GB
- Preboot21.6 GB
- VM, virtual memory21.5 GB · Managed by macOS
- Macintosh HD, macOS itself14.1 GB
- Recovery3.1 GB
Measured read-only in October 2026 on one Mac with a 500 GB internal disk running macOS 27. The sizes change with updates, memory use and what you store.
Why do disk images show up as disks?
Every disk image you open appears in the sidebar as a device of its own. On a developer's Mac, Xcode's simulator runtimes show up this way: on the Mac above, an iOS simulator runtime appeared as a separate 17.8 GB container.
Don't add those to your disk's total. The image is a file stored on one of your disks, so its space is already counted in that disk's used figure.
Can you delete any of these to free space?
No. Apple says you can't delete or erase your startup volume, and removing the support volumes would stop your Mac starting up or recovering. The space they take is part of running macOS. Free space by removing files from the Data volume instead.
Disk Utility storage figures: used, other volumes, free and purgeable
Select any volume, and the top of the window shows its capacity and a bar. That bar and the Info window are where Disk Utility answers how full a disk really is.
What does the bar show for a volume?
For an APFS volume, the bar splits the container into three: Used by the volume you selected, Other Volumes for every other volume in the same container, and Free. Above it, a line says how many volumes share the container.
Select a different volume in the same container and the same space moves between Used and Other Volumes. The free figure stays the same, because the volumes share it.
Why does each volume show the same free space?
Because APFS shares free space across the container. Apple's guide says the container's free space is allocated to each volume as it needs it. Apple's developer documentation adds that each volume includes that shared free space when it reports what's available.
So the free space you see on Macintosh HD and on Macintosh HD - Data is one pool, not two. Adding them up would count it twice.
Where do you see purgeable space?
Select a volume and click Info in the toolbar. The Info window lists available space as purgeable plus free, and each figure on its own. Apple describes purgeable space as space macOS can free when it's needed, made of files you can't remove yourself.
Local snapshots and downloaded iCloud Drive files that macOS can remove are common parts of it. The guide to purgeable space explains each one.
Why don't Disk Utility, Finder and Storage settings agree?
| Where | What it calls available or free | Best for |
|---|---|---|
| Disk Utility's bar | Free: unused space in the container | How much is really free now |
| Disk Utility's Info window | Available, split into free and purgeable | Seeing the purgeable part |
| Finder's Get Info or status bar | Available: free plus purgeable | Everyday checks |
| System Settings › General › Storage | Used by category, with available space | Seeing what kind of data it is |
They count different things, and none is wrong. The guide to why the storage numbers differ goes through each gap, and the post on checking storage on a Mac shows where to find each figure. Before a large copy or a macOS update, trust Disk Utility's free figure.
A worked example on one Mac
On the Mac measured above, with a 494 GB container, selecting Macintosh HD - Data showed about 421 GB used. Other Volumes came to about 60 GB: Macintosh HD, Preboot, Recovery and VM together. Free was about 10 GB, and the three figures add up to the container's capacity.
The same Mac's local snapshots were all ones that macOS updates make, with names starting com.apple.os.update, and none were Time Machine's. So on that Mac, removing local snapshots wouldn't have freed much; the space was in files on the data volume.
Why is Used bigger than all your folders?
A volume's used space includes things no folder shows: snapshots, the file system's own records, and hidden folders at the top of the volume. One of those keeps the earlier versions apps save as you edit, which the post on document revisions covers.
The catalog's entry for document versions rates that folder as managed by macOS: remove versions from the app with File › Revert To › Browse All Versions, never by deleting the folder.
The Info window: every detail about a disk
The Info button opens a window of facts about the selected device, container or volume. Most of them are technical, but a few answer storage questions directly.
What does the Info window show?
Apple says what it shows depends on the item. It can include:
- where the disk or volume is, internal or external
- its format, such as APFS or ExFAT
- its total capacity
- its available space, including free and purgeable space
- where the volume is mounted
- the disk's S.M.A.R.T. status, for disks that report it
What is S.M.A.R.T. status?
Apple describes it as the disk's general working condition. It's a health report from the disk itself. If Disk Utility reports a problem with it, back up the disk now, before relying on it for anything else.
Why does Info show used, purgeable and free differently on some disks?
For logical volumes, a kind of volume made outside Disk Utility, Apple says the used, purgeable and free figures depend on how much data the logical volume holds. You'll rarely meet them; most Macs and external drives today use APFS containers instead.
APFS snapshots in Disk Utility
Snapshots are the most common reason a disk is fuller than its files. Disk Utility is the only app Apple ships that lists them all, with their sizes.
How do you show the snapshots on a volume?
- Choose View › Show APFS Snapshots.
- Select a volume in the sidebar. Its snapshots appear in a table at the bottom of the window.
- Click the More menu and choose Show Columns to add or remove columns.
- When you're done, choose View › Hide APFS Snapshots.
Apple describes an APFS snapshot as a read-only copy of its parent volume, taken at a moment in time. A volume can have none or many.
Which columns matter for storage?
| Column | What it tells you |
|---|---|
| Name and Date Created | Who made it and when; Time Machine's names include a date |
| Private Size | Data that only this snapshot references |
| Cumulative Size | Data this snapshot and the ones before it reference |
| Tidemark | The highest block it uses, which limits how far the container can shrink |
| Kind | What sort of snapshot it is |
The definitions come from Disk Utility's own column descriptions. Private Size is the closest to what deleting one snapshot frees, but snapshots share most of their data with each other, so even that is a guide rather than a promise.
How do you delete a snapshot?
Select one or more snapshots in the table and click Delete Snapshot. Deleting is permanent: you can't restore anything from that snapshot afterwards.
For Time Machine's local snapshots, there's a gentler way. Choose Apple menu › System Settings, click General, then Time Machine, click Options, set Backup Frequency to Manually for a few minutes, then set it back. The guide to Time Machine local snapshots covers both ways.
Snapshots made by a backup app belong to that app; change its settings instead of deleting them behind its back. The post on APFS snapshots explains what makes each kind.
What about snapshots on a Time Machine backup disk?
On an APFS backup disk, each backup is itself a snapshot, so the table can be long. Leave those to Time Machine, which deletes the oldest when the disk is full. The post on deleting Time Machine backups covers removing them when you need to.
Why shouldn't you rename a snapshot?
The More menu has Rename, and Apple warns that a renamed snapshot may no longer be valid for its intended purpose. Leave the names as their owners made them.
Why is the snapshot list empty?
Because the selected volume has no snapshots, or because it isn't APFS: disks formatted as exFAT or Mac OS Extended can't have them. On your startup disk, select Macintosh HD - Data, where Time Machine's local snapshots are kept, rather than the system volume.
First Aid: what it can and can't fix
First Aid checks a disk's file system for errors in its formatting and directory structure, and repairs them. It's the right tool when a disk behaves strangely, not a way to free space.
When should you run First Aid?
When files won't open or copy, a disk won't mount, apps report disk errors, or the used space makes no sense even after you've accounted for the Trash and snapshots. On a healthy disk, First Aid finds nothing and changes nothing.
How do you run First Aid?
Apple's steps go from the inside out:
- Choose View › Show All Devices.
- Select the first volume, click First Aid, then Run, and follow the prompts. Repeat for each volume.
- Select each container and run First Aid on it.
- Select the storage device at the top and run First Aid last.
To check your startup disk, restart in macOS Recovery and open Disk Utility there. Apple says to check the data volume, Macintosh HD - Data, too.
What do First Aid's results mean?
| First Aid says | What to do |
|---|---|
| The disk appears to be OK, or was repaired | Nothing; Show Details has the full log |
| Overlapped extent allocation | Check the files listed; replace damaged ones |
| It couldn't repair the disk | Try again; then back up, erase and restore |
| The disk is about to fail | Back up now and replace the disk |
Overlapped extent allocation means two or more files share the same space, so at least one is likely damaged. Apple says many of them get aliases in a DamagedFiles folder at the top of the disk.
What can't First Aid fix?
Apple says plainly that Disk Utility can't detect or repair every problem a disk may have. It doesn't recover deleted files, it doesn't fix a failing disk's hardware, and it doesn't remove caches, snapshots or anything else that's taking space correctly.
If First Aid keeps failing, Apple's advice is to back up as much as you can, reformat the disk, reinstall macOS if it's the startup disk, and restore your files.
Adding a volume, with reserve and quota sizes
On an APFS disk, a new volume is the flexible way to keep things apart: a second macOS for testing, a volume for backups next to your files, or a volume for one project. It shares the container's free space instead of needing its own.
Should you add a volume or a partition?
A volume, in almost every case. Apple says you shouldn't partition your disk in most cases, and suggests creating several APFS volumes in one partition instead. A partition has a fixed size; a volume grows and shrinks as you use it.
How do you add an APFS volume?
- Select an existing APFS volume in the sidebar.
- Click Add Volume in the toolbar.
- Enter a name and choose a format, such as APFS or APFS (Encrypted).
- To control its space, click Size Options… and enter a reserve size, a quota size or both.
- Click Add, then Done.
What do reserve size and quota size do?
Disk Utility's own description says the optional reserve size ensures that amount of storage stays available for the volume, and the optional quota size limits how much storage it can take. Apple says you need them only to manage the container's space by hand.
A reserve suits a volume that must never run out, such as one for an app's working files. Photoshop, for example, lets you choose which disk holds its scratch files, and the post on a full Photoshop scratch disk covers that choice.
A quota suits a volume that could otherwise take everything, such as one an app fills with recordings or caches. Neither can be more than the container holds.
Where does the space go when you delete a volume?
Back to the container's shared free space, for the other volumes to use. Apple says deleting a volume erases all its data permanently and removes it from the container; erasing a volume instead leaves it in place, empty.
If Delete Volume is dimmed, the volume is in use and can be deleted only from Disk Utility in macOS Recovery. A volume that's part of a volume group offers to delete the whole group or only that volume.
Erasing, partitioning and restoring: read this first
These are the controls that destroy data. Each has a reason to exist, and none frees space without erasing what's there, so copy anything you want to keep to another disk first.
What's the difference between erasing a volume and a device?
Erasing a volume removes its files and leaves an empty volume in its container. Erasing a device removes everything on the disk, every volume and partition, and lets you choose a new scheme and format. Apple says the Scheme menu appears only when the top-level device is selected.
Apple's erase steps set the scheme to GUID Partition Map, the scheme Apple recommends for all Intel-based and Apple silicon Macs. Master Boot Record is for compatibility with Windows PCs.
Which format should you choose?
Apple's guide recommends APFS when you don't need encryption or case-sensitive names, and APFS (Encrypted) when you do want encryption. For a disk shared with Windows, it suggests MS-DOS (FAT) for 32 GB or less and ExFAT for anything larger.
The post comparing APFS and exFAT goes through which suits each kind of drive, including Time Machine disks and drives you share with a PC.
When does partitioning make sense?
Rarely, on a Mac. A Windows-formatted section of an external drive is one case. On an Intel-based Mac, Apple says to use Boot Camp Assistant, not Disk Utility, to install Windows or to remove its partition.
When you click Partition, a pie chart shows each partition's used and free space. Apple says you can enlarge a partition only by deleting the one after it, which erases that one's data, and you can't enlarge the last one on a device.
What does Restore do?
Restore makes an exact copy of one volume on another. Apple says every file on the destination volume is erased first. It's a way to clone a disk, and a way to lose one if you pick the wrong destination, so check the names twice.
Can Disk Utility make your Mac's disk bigger?
No. It can divide the space on a disk between volumes and partitions, but never add to it. The post on upgrading a Mac's storage covers the options that do give you more room.
What about secure erase?
Apple says secure erase options are offered only for some kinds of disks, and not for solid-state drives. For an SSD, Apple's suggestion is to turn on FileVault when you start using it, so erased data stays unreadable.
Disk images: files that act like disks
A disk image is a single file that holds a whole volume. Disk Utility makes them, opens them, converts them and resizes them, and each one you open appears in its sidebar like a disk.
How big is a new disk image?
It depends on how you make it. Apple's guide says an image made from a whole device includes its free space, so an 80 GB device holding 10 GB of data makes an 80 GB image. An image made from a folder holds only the data, so the same 10 GB makes a 10 GB image.
Which image format should you pick?
| Format | What Apple says about it | Space it takes |
|---|---|---|
| Sparse bundle | Read-write, grows with its data, stored as many files | Grows as you add data |
| Apple Sparse Image (ASIF) | Read-write, a modern sparse image | In proportion to its data |
| Read-only | Can't be changed after it's made | Fixed |
| Read-only compressed | Can't be changed, stored compressed | Fixed, smaller |
| DVD/CD master | For burning to a disc | Fixed |
Choose File › New Image › Blank Image for an empty one, or Image from Folder to pack up a folder. Apple says you can't make images of individual APFS volumes, or of APFS containers on Apple silicon Macs and Intel Macs with a T2 chip.
Can you shrink a disk image?
Some formats, yes. Eject the image, choose Images › Resize, select it, enter a new size and click Resize. Apple notes that not all formats support writing and resizing, and doesn't say which. A sparse bundle grows with what you add, and Apple's guide doesn't say it shrinks when you delete files inside it.
Why does an image you didn't open appear in the sidebar?
Some apps mount their own images. Xcode's simulator runtimes, for example, are disk images macOS mounts so simulators can use them. Leave those to the app that mounted them.
Common storage questions Disk Utility answers
Most people open Disk Utility with one question. Here are the common ones, and which part of the window answers each.
Is my disk really full, or is it purgeable space?
Click Info and compare free with purgeable. If purgeable is large, macOS can make room by itself as space is needed; the free figure is what's unused right now. If free is low and purgeable is small, the space is in real files.
Why is my external drive full when it looks empty?
Select its container with all devices showing. A large Other Volumes figure means a second volume, often Time Machine's, holds the space. If there's no second volume, show snapshots and check them. The post on an external drive that's full with no files covers every other cause.
Will a macOS update fit?
Check the free figure in the Info window for Macintosh HD - Data. If it's short but purgeable is large, removing Time Machine's local snapshots usually gives the room back. Disk Utility doesn't say how much an update needs; the update itself tells you.
Why does a disk show less capacity than its label?
Apple says drive makers count 1 GB as 1 billion bytes, and that only OS X Leopard and earlier counted in binary units. So Disk Utility and the label use the same units, and the small gap is the space formatting and the file system take, not missing storage.
What's this volume I don't recognize?
Select it and click Info for its format and where it's mounted, then Mount it if it isn't, and look inside in Finder. Many are a second macOS, a backup volume, or a disk image an app mounted. Don't delete one until you know what it is; deleting erases it.
Mistakes to avoid in Disk Utility
- Erasing or deleting to "clean up". Both remove data for good; neither is a cleanup tool.
- Adding up every volume's free space. Volumes in one container share it, so you'd count it several times.
- Partitioning instead of adding a volume. Partitions are fixed; volumes share space.
- Deleting snapshots you can't name. Let the app that made them manage them.
- Running First Aid to free space. It repairs; it doesn't remove anything.
How the app does it
Wombit shows what's using your storage, explains every item in plain language, and clears it safely: Trash first, undoable and logged. It covers the half Disk Utility doesn't: which files and folders use the space and what each one is. Volumes, partitions and First Aid stay in Disk Utility.
Its space meter, in the app and in the menu bar, shows what's available and how much of that is really free. The Why the numbers differ panel beside it says how much of the gap is purgeable and how many local snapshots there are.
System Data, explained splits that one number into named buckets, such as local snapshots, caches, logs and swap, and shows how much it couldn't explain. The Local Snapshots page lists every snapshot, when it was made and which app made it.
Hourly snapshots of your startup disk that Time Machine keeps on the disk itself, so you can restore files even without your backup disk.
Managed by macOS · Runs tmutil for Time Machine's own snapshots, through the helper
/
System/ Volumes/ Data/ .DocumentRevisions-V100 Earlier versions of documents that apps like Pages, TextEdit and Preview save as you work, so you can go back to them.
Managed by macOS · Explained only: the app shows you how
Local snapshots and document versions are Managed by macOS: explained, handled through macOS's own mechanism, never moved. When you choose, the app removes only Time Machine's own snapshots, with Time Machine's own tool and an administrator's password, and measures the available space before and after.
The analyzer, the space meter, System Data explained and the snapshot list are free. Removing Time Machine snapshots and Cleanup are PRO: one payment of $4.99 with lifetime access. Every Pro tool's review is free to open, so you see what would go and why before you buy.
Frequently asked questions
How do I see all my disks and volumes in Disk Utility?
Choose View › Show All Devices. The sidebar then lists each storage device with its containers and volumes, instead of only the volumes. Apple says some tasks, such as erasing a whole device, are possible only in this view.
What does Other Volumes mean in Disk Utility?
It's the space used by the other volumes in the same APFS container as the one you selected. On a Mac's startup disk that's mostly Macintosh HD, Preboot, Recovery and VM. On an external drive, it's often a Time Machine backup volume sharing the drive.
Where does Disk Utility show purgeable space?
Select a volume and click the Info button in the toolbar. Its Info window lists available space as purgeable plus free, along with each figure on its own. Purgeable space is space macOS can free when it needs to; you can't remove those files yourself.
Does First Aid free up storage space?
Not usually. First Aid checks and repairs the file system's formatting and directory structure. It can fix space reported wrongly because of damage, but it doesn't remove caches, snapshots or files, so on a healthy disk the free space stays the same.
Is it safe to delete a snapshot in Disk Utility?
It's permanent: you can no longer restore anything from that snapshot. For Time Machine's local snapshots, Apple's own way is to let Time Machine remove them, or set Backup Frequency to Manually for a few minutes. Delete a single snapshot in Disk Utility only when you know what made it.
What is the difference between reserve size and quota size?
Both are optional when you add an APFS volume. A reserve size keeps that much of the container's space available for the volume, whatever the others use. A quota size limits how much space the volume can take.
Should I partition my Mac's disk or add a volume?
Add a volume. Apple says you shouldn't partition your disk in most cases, and suggests several APFS volumes in one partition instead, since they share free space. A partition has a fixed size, and changing it later can mean erasing data.
Can Disk Utility delete Macintosh HD - Data or Preboot to free space?
No, and you shouldn't try. Apple says you can't delete or erase your startup volume, and the Data volume holds your files, apps and settings. Preboot, Recovery and VM are part of how your Mac starts up and runs.
Sources
- View all devices or only volumes in Disk Utility on Mac · Apple
- Get detailed information about a disk in Disk Utility on Mac · Apple
- View APFS snapshots in Disk Utility on Mac · Apple
- Repair a storage device in Disk Utility on Mac · Apple
- Add, delete, or erase APFS volumes in Disk Utility on Mac · Apple
- Create a disk image using Disk Utility on Mac · Apple