Why deleting frees space only after maintenance
When you delete snapshots or remove files from them, the repository doesn't get smaller straight away. This page explains what kopia does with deleted data, and why the space comes back a few days later.
What a delete changes
Kopia stores your files as pieces, packed together into larger files in the repository's storage. A snapshot doesn't hold the pieces themselves. It holds a list of which pieces make up each file.
So a delete changes only those lists:
- Deleting a snapshot removes its list.
- Removing files from snapshots writes each snapshot again, without those files.
The pieces stay in storage. Some are still used by other snapshots, other paths or other computers' backups. Others are now unused, but kopia doesn't know that yet.
What maintenance does
Full maintenance finds the unused pieces and removes them. It runs in steps:
- It goes through every snapshot and marks the pieces that none of them uses.
- On the next run, it checks again. On the run after that, pieces that are still unused are dropped.
- Packed files that now hold mostly unused pieces are rewritten, keeping only the pieces in use.
- Packed files that hold nothing in use are deleted from storage. This is when the space comes back.
Quick maintenance only tidies kopia's own index and cache. It frees little space.
Why kopia waits
Another computer, or another app, may be backing up into the same repository at the same moment. A backup that is still running can use a piece that looks unused, because its snapshot isn't saved yet. If kopia deleted that piece at once, the backup would be damaged.
So with kopia's default Normal safety:
- A piece is dropped only on the run after two full maintenance runs, at least 4 hours apart, have both found it unused.
- Data written in the last 24 hours is never collected.
- A packed file is deleted from storage only when it's more than 24 hours old.
Full maintenance runs once a day by default. Together, these rules mean most of the space comes back two or three days after a delete.
An example
You delete a 50 GB folder from all snapshots on Monday at 10
.| When | What happens | Repository size |
|---|---|---|
| Monday 10 | The delete finishes. The snapshots no longer list the folder | Unchanged |
| Monday night | Full maintenance marks the folder's pieces as unused | Unchanged |
| Tuesday night | Full maintenance finds them unused again | Unchanged |
| Wednesday night | Full maintenance drops them. Packed files that hold nothing in use are deleted, on this run or the next | Shrinks as old packed files go |
| Thursday or Friday night | Packed files that held both kinds are rewritten, and the old copies are deleted on a following run | About 50 GB smaller |
The exact days depend on when maintenance runs on your repository.
Getting it back sooner
- Run full maintenance by hand: Run maintenance… in the Repository tab (Maintenance).
- With Safety: None, kopia skips its waiting rules and deletes unused data now. Use it only on a repository that only you use, when no backup is running.
Why the freed space can differ from Reclaimable
KopiaLens's Reclaimable figure counts the pieces nothing else uses. The space that storage gives back can be slightly different:
- Kopia frees space packed file by packed file, so a few unused pieces can wait in a packed file that is still mostly in use.
- Snapshots taken after the last index run can use some of the same pieces.
- Kopia's own index and metadata take space too.