---
title: Why is PhotoStructure rebuilding my library?
url: https://photostructure.com/guide/library-rebuilds/
description: Learn about PhotoStructure library rebuilds
date: 2020-05-17
keywords: library-rebuild, deduplication, metadata, previews, video-transcoding
---


When you upgrade to a new version of PhotoStructure, you may see a progress bar
with content like this:

{{< figure src="/img/2020/06/rebuild.jpg" >}}

## 🔄 What's going on here?

New versions of PhotoStructure frequently introduce new features that require revisiting the photos and videos in your library.

Library rebuilding happens in several steps:

1. File metadata is updated.
2. Assets are regrouped.
3. Asset previews are refreshed.
4. New taggers may be applied.

### Updating file metadata

PhotoStructure extracts and stores metadata about the files in your
library in a database. This database makes browsing and library synchronization fast, and is used to [deduplicate](/faq/what-do-you-mean-by-deduplicate/) your photos and videos.

### Regrouping assets

PhotoStructure applies [deduplication](/faq/what-do-you-mean-by-deduplicate/)
heuristics for all files associated to each asset.

The number of assets in your library may increase or decrease as this step progresses.

### Refreshing previews

PhotoStructure examines and rebuilds the previews, thumbnails, and transcoded
videos in your library to make sure they are up to date.

This may mean your library takes a bit more or less disk space than it did
before rebuilding.

### Curating assets

New versions of PhotoStructure may come with new "curators," which add tags to your assets automatically.

## ⚠️ Please note

If you are **not** using [automatic
organization](/getting-started/automatic-library-organization/):

1. Plug in the
   external hard drives and mount the remote file systems that you’ve already imported into
   your library, and then
2. [Restart PhotoStructure](/faq/how-to-start-and-stop-photostructure/).
3. Leave these volumes turned on and mounted until your library finishes
   rebuilding.

This gives PhotoStructure a chance to visit those files and update your library
database.

If you are using automatic organization, you can skip these steps.
PhotoStructure will automatically backfill any missing file metadata by using
the matching copy in your library.

## ⏳ Why does PhotoStructure wait until the rebuild is complete before importing any new files or directories?

Correct asset [de-duplication](/faq/what-do-you-mean-by-deduplicate/) during file
imports and syncs require your library’s metadata to be up to date. By updating
your library before running any sync jobs, PhotoStructure is ensuring your
library stays correct and coherent.

## ❓ Can I exit PhotoStructure or reboot my computer while my library is being rebuilt?

Yes. As soon as you [restart
PhotoStructure](/faq/how-to-start-and-stop-photostructure/), you’ll see the
rebuild process pick up where it left off.

## ⚠️ Can I rebuild my library on multiple computers at the same time?

No. PhotoStructure can only run on one computer concurrently. If you’ve imported
files from different computers, let the rebuild complete on one computer, shut
down PhotoStructure, and start it on the next computer.

## See also

[What's the difference between "rebuild" and "resync"?](/faq/sync-vs-rebuild/)