Two-way sync and the First run box

A two-way sync — Bidirectional sync in Data Transfers — needs one extra step the first time: tick First run for this pair in Advanced options. That first run sets the starting point Storage Studio compares against from then on. After it, the box must never be ticked again for the same two folders.

Why there's a first run

A two-way sync carries changes in both directions, including deletions. To know what changed — and on which side — it compares each folder with how both looked at the end of the previous run. On the very first run there is no previous run, so the first run builds that starting point by bringing the two folders together. Every later run works from it.

Setting up a two-way sync

1. Check the two folders. Ideally one of them is empty, or both already hold the same files. If both have different files in them, the first run brings them together, so make sure that's what you want.
2. In Data Transfers, click New Transfer and choose Bidirectional sync.
3. Fill in Source and Destination. For a two-way sync it doesn't matter much which is which, but keep them the same way round if you ever set it up again.
4. Open Advanced options and tick First run for this pair. The box appears only for Bidirectional sync.
5. Optionally tick Dry run (preview only) to rehearse it first — see Trying a transfer first with Dry run. If you do, set the transfer up again afterwards with the box ticked and Dry run off for the real first run.
6. Choose a Schedule if you want it to repeat, then click Start Transfer.

From then on, use Sync again or the schedule. Both always run without the first-run box, even when the original transfer had it ticked, so you can't tick it again by accident.

%% caption: When to tick the First run box
flowchart TD
  A[Setting up a Bidirectional sync] --> B{Has this exact pair of folders ever completed a two-way sync?}
  B -->|No, this is the first time| C[Tick First run for this pair]
  B -->|Yes| D[Leave it unticked]
  C --> E[Later runs: Sync again or the schedule]
  D --> E
  E --> F[These never use the First run box]

What happens if it's ticked again

Ticking the box on a later run throws away the starting point and builds a new one. The app warns that this would silently overwrite one side with the other — a change or deletion you made on one side since the last run could be undone by the other side. That's why the warning under the box is shown in orange, and why repeat runs never carry it.

If you've already ticked it again by mistake, look through both folders for anything that came back or changed, and restore what you need from a backup — see Restoring from a backup.

When the same file changes on both sides

If one file was edited on both sides between two runs, Storage Studio can't know which edit you want. It records the clash as a conflict in the transfer's Log. To avoid conflicts:

• Let a sync finish before you edit the same file in the other place.
• Schedule runs often enough that the two sides don't drift far apart — see Scheduling a transfer.
• Avoid opening the same document on both sides at the same time.

Starting again with a new pair

The first-run step belongs to a pair of folders. If you change either folder — a different destination, or a renamed source — that's a new pair, and its first run needs the box ticked again.

See also: Copy, Move, Sync or Two-way sync · Two-way sync · Sync again and Run again · Files that change during a transfer