Trying a transfer first with Dry run

A dry run rehearses a transfer without changing anything. Storage Studio looks at the source and the destination, works out what it would copy, move or delete, and writes that into the transfer's Log — but no file is copied, moved or removed. It's the safe way to check a Sync (one-way) before it deletes anything at the destination.

Running one

1. In Data Transfers, click New Transfer and set up the transfer as you normally would.
2. Tick Dry run (preview only) at the bottom of the sheet, next to Start Transfer.
3. Click Start Transfer.

The dry run appears in the list like any other transfer and usually finishes much faster than the real thing, because nothing is sent. It still has to look at both sides, so a very large folder can take a little while.

Reading the result

Select the finished dry run and look at the Log at the bottom of its details. It lists each file the transfer would have touched, each one noted as skipped because this was a dry run. Look in particular for:

• Files you didn't expect to be included — check the source path is the folder you meant, not its parent.
• Deletions — for a Sync (one-way) or a Bidirectional sync, any file listed as deleted would really be removed on a real run. If something there should be kept, it's in the destination but not the source: copy it into the source first, or choose a different destination folder.
• Nothing at all — the two sides already match, or the source path is empty or wrong.

The Log keeps only the most recent lines, so for a big folder it may not show every file — try a dry run on a smaller sub-folder if you need to see everything. Your Mac's files and the destination are exactly as they were before the dry run.

%% caption: Using a dry run before the real transfer
flowchart TD
  A[Set up the transfer] --> B[Tick Dry run and start it]
  B --> C[Read the Log in its details]
  C --> D{Does the list look right?}
  D -->|Yes| E[Click Run again or Sync again to do it for real]
  D -->|No| F[Fix the source or destination and try another dry run]
  F --> B

Doing it for real

When you're happy with the preview, select the dry run and click Run again (or Sync again for a sync). A repeat run always switches Dry run off, so it performs the transfer for real with the same source, destination and settings. See Sync again and Run again.

Things to know

• A scheduled dry run stays a dry run. If you tick Dry run and also pick a Schedule, every scheduled run is a rehearsal too, and nothing is ever transferred. Set up the real schedule without Dry run. See Scheduling a transfer.
• Files can change in between. A dry run describes the folders at the moment it ran. If files change before the real run, the real run works from what's there then.
• Large downloads aren't split into pieces during a dry run, because nothing is downloaded.
• The first run of a two-way sync is the exception. A dry run with First run for this pair ticked is a sensible check, but don't use Sync again afterwards: a repeat never carries the First run for this pair box. Instead, set the transfer up again with that box ticked and Dry run off. See Two-way sync and the First run box.

See dry run in the glossary.

See also: Copy, Move, Sync or Two-way sync · Data Transfers · A transfer failed