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One copy, and Removed Files

One up-to-date copy

Your backup drive holds one copy of your files, as they were at your last backup. This is called a mirror. When you back up again, Deucalion compares your computer with the backup and copies only:

  • files that are new on your computer;
  • files that changed since the last backup.

Files that didn't change are not copied again, so later backups are much faster than the first one.

Nothing is thrown away: Removed Files

A mirror has a risk: if you delete a file by mistake and then back up, the backup would lose it too. Deucalion avoids this. When a backup would replace or remove something on the drive, it moves the old copy to Removed Files instead of deleting it:

  • When a file changed, the previous version goes to Removed Files and the new version takes its place in the backup.
  • When a file was deleted from your computer (or you left it out), its copy in the backup goes to Removed Files.
flowchart LR
    A["report.odt<br/>changed on your computer"] -->|backup| B["Backup: the new report.odt"]
    B -. "the old version moves to" .-> R["Removed Files<br/>(_removed/2026-10-11_143005/…)"]
    C["photo.jpg<br/>deleted on your computer"] -->|backup| R

On the drive, Removed Files is the folder Deucalion-Backup/_removed. Each backup that moved something there gets its own folder named after the date and time it started, for example _removed/2026-10-11_143005/. Inside, files keep their usual folders (_removed/2026-10-11_143005/home/Documents/report.odt), so you can find and open them directly.

Nothing in Removed Files is ever deleted by Deucalion. Only you can empty it, in the app's Removed Files page or with deucalion removed empty. This is how you free space when the drive fills up: see Free space on the drive.

Turning off old versions

In Settings, the switch Keep old versions of changed files decides what happens to the previous version of a file that changed. When it is off, the old version is replaced directly instead of going to Removed Files. Files deleted from your computer still go to Removed Files. It is on by default.

What this is not

Removed Files is not a full history: it holds the versions that were replaced or removed by each backup, but not a complete picture of your computer on each day. If you need to go back to a specific day, look in the folder of the backup that ran right after that day. Snapshot history is planned for a later version.