Where did my space go?

Storage Studio keeps an eye on your free space all the time, so when it drops you can find out why. If space falls quickly, it works out which app or folder grew and warns you when you're on course to run out. And for any stretch of time on your storage chart, it can list what changed, biggest first.

The watch in the background

Every 30 seconds, Storage Studio checks how much free space your Mac has. This is a single quick reading: it doesn't scan your disk and costs almost nothing. Only when free space falls fast does it look further:

• A sudden drop: 5 GB or more within 15 minutes.
• A steady drain: 20 GB or more within 3 hours.

When either happens, Storage Studio measures the likely places once to find what grew, and keeps a record of it.

%% caption: From a drop in free space to a notice
flowchart TD
  A[Free space checked every 30 seconds] --> B{Did it fall fast?}
  B -->|No| A
  B -->|Yes| C[Find which apps and folders grew]
  C --> D{Was it Storage Studio's own work?}
  D -->|Yes| E[Noted in Job Insights only]
  D -->|No| F{Is the space held by automatic backups?}
  F -->|Yes| G[Explained, with Release that space]
  F -->|No| H{Will the disk fill within about a week at this rate?}
  H -->|Yes| I[Notification naming the cause]
  H -->|No| J[Recorded quietly for later]

When you're told, and when you aren't

Storage Studio tries hard not to cry wolf. A big drop on a Mac with lots of room left isn't a problem, so you're only interrupted when the rate means you could run out of space in about a week or less. Very short bursts are recorded but never interrupt you on their own. The notice says how fast the space went, what the biggest change was, and roughly how many days of room you have left at that rate.

Everything else is still recorded, so you can look it up later in Job Insights under Storage watch, and on the storage chart. A drop caused by Storage Studio's own work (a move in progress, for example) is noted there as Free space dropped while Storage Studio was working. That was us.

Each problem is reported once. Further growth from the same place updates the same notice rather than adding new ones, and a place that's already been reported won't be reported again for 6 hours unless it grows by much more than before.

When the space is held, not lost

Often the space hasn't really gone. After files are moved or deleted, your Mac keeps them in its automatic backups (local snapshots) for a while, so free space can drop even though nothing new was written. When that's the cause, the notice says so: Your free space will come back on its own. When the space held is large enough, the notice carries a Release that space button, which asks your Mac to let that space go. Releasing it doesn't delete anything you still have. Your Mac decides how much it lets go of, so you're told afterwards exactly what came back, including when it kept hold of the space for now. See Why deleting files doesn't always give the space back.

Asking about any period

Open the More menu (•••) → Where Did My Space Go…. It opens your Storage Profile, where the Free space over time chart sits under Your storage over time. Pick a range, or drag across part of the chart, and the panel underneath explains What changed in this period:

• each app or place that gained or lost space, biggest first, named in plain words;
• the space your Mac is holding in automatic backups, as its own line, with Review and release…, which lists those backups first and then offers Release space;
• a Not accounted for line when Storage Studio can't explain part of the change, rather than guessing.

Most lines carry a button to the screen that deals with them, such as Show me or Free up space. The Trash line offers Open Trash, because emptying it can't be undone and is yours to do. If a period can't be explained because no reading was taken back then, Measure now records where your space is today so that later periods can be.

See also: Storage charts and history · Storage Inspector · Emergency Space · Background Activity and Job Insights · Local snapshots