Background duplicate scans

With Auto-scan on, Storage Studio looks for duplicate files in the background so the results are ready when you open the Duplicates window. Scanning your Mac waits until it's idle, plugged in and cool; checking a cloud account is lighter and only waits for a short pause. A background scan only ever finds duplicates — nothing is removed without you approving it.

Auto-scan is on by default for This Mac, for iCloud Drive and for each cloud account. You'll find the switch in the header of each source in the Duplicates window; turn it off for any source you'd rather scan only with Scan now.

When a background scan runs

Storage Studio checks whether it's a good moment about every 15 minutes, starting shortly after launch. Each source is scanned at most once every 6 hours.

%% caption: How Storage Studio decides whether a background duplicate scan can start
flowchart TD
  A[Regular check] --> B{Is the Mac in a power-saving or busy performance mode?}
  B -->|Yes| P[Paused - try again later]
  B -->|No| C{Running hot or Low Power Mode on?}
  C -->|Yes| P
  C -->|No| D{Which source?}
  D -->|This Mac| E{Plugged in and no input for 2 minutes?}
  D -->|Cloud account| F{Battery not low and a short pause in your typing?}
  E -->|Yes| G[Scan this Mac]
  F -->|Yes| H[Scan the account that waited longest]
  E -->|No| P
  F -->|No| P

This Mac reads a lot of your disk, so it waits until you've been away from the keyboard and mouse for about two minutes, the Mac is on power, it isn't running hot and Low Power Mode is off.

Cloud accounts only read a list of file fingerprints over the network, so they're gentler: they wait for about half a minute without typing or mouse use, and they can run on battery unless the charge is below 40%. Only one account is scanned at a time, the one that has waited longest going first. Some kinds of account — S3-compatible storage and Google Photos among them — are never scanned in the background, only when you click Scan now.

iCloud Drive is refreshed when you open the window or select it, rather than on the timer.

When your Mac is in Survival or Minimum performance mode, background duplicate scans pause. Scan now always works, whatever the mode — it's something you asked for, not background work.

Staying out of your way

Even once a scan starts, it works slowly on purpose. The disk reads give way to your own work, each file is followed by a short pause, and on your Mac, files that haven't changed since an earlier scan aren't read in full again. See Why Storage Studio works slowly on purpose.

What the status line means

Smart Care and duplicates

If Let Smart Care clean duplicate files is on — in Settings → Rules → Global overrides, on by default — Smart Care uses the latest background results when it runs. After its normal run it can show Duplicate files found with the number of sets and the space they take, and offers Move extras to Trash, Review first… or Skip.

Smart Care never starts a scan of its own. It keeps the recommended copy of each set, leaves out any set where a copy changed in the last 7 days, and only offers when there's enough to be worth it. Nothing is removed until you click. Removed extras go to the Recycle Vault like any other duplicate removal, so they can be restored.

See also: Finding and removing duplicates · Duplicates in your cloud accounts · Background Activity and Job Insights · Battery and power