Open Disk Utility, select your drive, and there it is: a category called Other Volumes in Container using a large slice of the disk. It looks like something is wrong. It is not. This is how APFS reports storage, and understanding it saves a lot of pointless deleting.
Containers and volumes, briefly
Before APFS, partitions were fixed. If one had 20GB free and another was full, the free space was unusable. APFS changed that with containers: one pool of storage shared by multiple volumes, which grow and shrink as needed.
Your Mac's internal drive is a single container holding several volumes. Disk Utility lists the ones you do not interact with directly under Other Volumes in Container, which is why the label is confusing: they are not one thing, they are five or six.
What is actually in there
- System: the read only copy of macOS. Around 10GB to 15GB depending on version.
- Data: your files. This is the volume you actually use, and it is also the one that grows.
- Preboot: boot configuration. A few hundred megabytes.
- Recovery: the recovery environment used when startup fails. Around 1GB.
- VM: swap and virtual memory. Grows with memory pressure.
- Update: staging space for macOS updates, in use only around an update.
Snapshot space is counted here too, and it is usually the largest variable.
The snapshot effect
Local Time Machine snapshots are point in time copies of your disk. The clever part is that they share unchanged data. The confusing part is that deleting a large file does not return space while a snapshot still references it.
tmutil listlocalsnapshots /
tmutil listlocalsnapshots / | wc -lIf the second command returns a number above five, snapshots are likely holding tens of gigabytes. macOS thins them automatically, but not on a schedule you control. To remove one you no longer need:
sudo tmutil deletelocalsnapshots 2026-08-01-101530Do this only with a working external backup. Snapshots exist to protect you, which is easy to forget while chasing free space.
How to check what is really using the space
Disk Utility reports volumes, not folders, so it cannot tell you that Library holds 40GB and Projects holds 21GB. For that you need a view of the file system itself. The terminal approach:
df -h /
du -sh ~/* 2>/dev/null | sort -hr | head -12The visual approach shows the same data as rectangles sized by content, which is faster to read when a single folder has grown to dominate the drive.
macoptimize works at the file level, which is the level where decisions are actually made. It shows which folders inside your home directory hold the space, tracks free space over time on the Status tab, and lists the reclaimable caches in one place, so the number Disk Utility reports becomes an explanation instead of a mystery.
What you can safely do
- Delete local snapshots when space is tight and backups are current.
- Clear caches and developer output, which is where the real growth happens.
- Restart the Mac to shrink swap files after a memory heavy session.
- Leave the System, Preboot and Recovery volumes alone. They are not taking space you can recover, and removing them breaks startup.
What you should not do
Do not try to delete a volume from the container to free space. Removing volumes does not return space to the pool in a way you can use, and deleting the wrong one leaves a Mac that will not boot. If the container shows far more used space than your files account for, snapshots and swap are the explanation, not a hidden partition.
The commands that answer this properly
Everything that follows comes from four commands. They are read only apart from the snapshot delete, and they tell you more than the Storage panel ever will:
diskutil apfs list
tmutil listlocalsnapshots /
df -h /
du -sh /System/Volumes/Data/.* 2>/dev/nulldiskutil apfs listshows every volume in the container with its role and how much space it occupies.tmutil listlocalsnapshotslists the hourly snapshots that hold onto deleted data.df -h /gives free space as the system sees it, which differs from what Finder reports.- The
duline measures the hidden folders inside the Data volume, which is where the unaccounted space usually hides.
The volumes in the container, and which ones matter
| Volume | Role | Touch it? |
|---|---|---|
| Macintosh HD | Read only system volume | Never |
| Macintosh HD - Data | Your files and the hidden folders | Yes, selectively |
| VM | Swap and sleep images | Managed by the kernel |
| Preboot, Recovery | Boot and recovery helpers | Never |
| Update | Staged system updates | Only leftovers |
| com.apple.TimeMachine.* | Local snapshots | Yes, via tmutil |
The four at the top are measured in megabytes and are not your problem. The ones worth attention are the Data volume, the snapshot volumes, and the Update volume when it holds a staged installer.
Thinning snapshots, in practice
tmutil listlocalsnapshots /
tmutil thinlocalsnapshots / 1000000000000 4The second command asks the system to free up to that many bytes (one terabyte, a ceiling rather than a target) and stops once urgency level 4 is reached, which means it also touches snapshots that would normally be retained. On a Mac with 60GB of local snapshots it typically returns a large part of that within a minute.
You can also delete a specific one by name, which is more predictable:
sudo tmutil deletelocalsnapshots 2026-09-14-120000Snapshots are not backups on their own, but they are the reason deleted files sometimes refuse to release space for up to a day.
What happens if you erase the wrong volume
Deleting a volume in Disk Utility can take your Mac down. The Preboot, Recovery and VM volumes are required for the system to boot and to sleep correctly. Erasing them can leave a Mac that will not start without a reinstall. If you are troubleshooting the container, do it with the commands above rather than by deleting volumes, and work from a backup if you must go further.
The one safe destructive move, in a situation where free space is genuinely stuck, is erasing the Mac and restoring from a backup. That resets the container completely. It is worth doing when the numbers are unexplainable, and never worth doing as a first attempt.
FAQ
Is Other Volumes in Container junk I can delete?
No. That label covers macOS system volumes, your Data volume, swap, and local snapshots. Two parts are worth reducing, the snapshots and staged update leftovers, and the rest is what makes the Mac boot and sleep. There is no single folder behind the number.
Why does the total not match my free space?
Because several of those volumes are thin provisioned and share free space, Finder rounds its numbers, and snapshots hold onto data that applications have already deleted. df in Terminal and the Storage panel in System Settings measure the same disk and frequently disagree by tens of gigabytes.
Should I erase and reinstall to fix it?
Only as a last resort and only with a tested backup. It does reset the container and the number, but it costs hours and it does not prevent the same buildup from happening again, since snapshots and caches grow back on every Mac that is used.
Can I turn off local snapshots permanently?
You can, and it is a bad trade. Local snapshots are what make Time Machine restores possible between hourly backups and they hold deleted files for a day. Thinning them occasionally is reasonable, disabling them entirely removes a safety net to fix a cosmetics problem.
Which command should I run first?
diskutil apfs list, because it shows the container layout and the sizes in one place. Then tmutil listlocalsnapshots to see whether snapshots are holding anything. Those two answers decide whether you have a snapshot problem or a real data problem.