# Why a NotchStar Disk scan can be slow

> Scans read real files: sizing folders, hashing duplicates and recompressing media all take time on big libraries. Here is what each one does.

Canonical: https://www.notchstar.com/help/why-notchstar-disk-scan-is-slow/
Last updated: 2026-11-04

Published 2026-11-04.

Disk scans are slow when you have a lot of files, because they read real data from the disk. No timings have been measured, since they depend on how many files you have and what kind of drive holds them. This page says what each scan does so you can see where the time goes.

## What each scan does

| Section | Work | Why it takes time |
|---|---|---|
| Overview | Adds up the size of every item in caches, logs, Xcode data and Downloads | Caches can hold very many small files |
| Space | Sizes every folder in your home folder, four at a time | The Library folder is often the largest thing you own |
| Find | Walks your home folder and matches names | Every file and folder is looked at |
| Duplicates | Groups by size, hashes the ends, then hashes the whole file | Full hashing reads each candidate completely |
| Apps | Measures each app and its leftovers | Large apps are big folders |
| Compress | Re encodes each chosen file | Video encoding is the heaviest work in the tab |

## Things that make it slower

- External or network drives, or folders synced by a cloud service.
- A first scan of Documents, Desktop or Downloads, when macOS asks for access.
- Very large media libraries in Movies and Pictures.
- Other heavy work on the Mac at the same time.

## Why it is built this way

Most scans run as low priority background tasks, and they start only when you press a button. Nothing runs in the background. Results appear as they are measured in Space, so you can start reading before it finishes.

## What to do

Scan one section at a time, and begin with Space to see where the weight is. Duplicates is narrower: only files of 1 MB or more in six folders. See [how duplicates are found](https://www.notchstar.com/help/find-duplicate-files-notchstar/) and [how to find the biggest folders](https://www.notchstar.com/help/find-biggest-folders-notchstar/). The [Disk feature page](https://www.notchstar.com/features/disk/) lists everything the tab does.

## Quick answers.

### Can I stop a compression?

Yes. Compress has a Stop after this one button, which ends the run after the current file.

## Keep reading.

- [Disk space, duplicates, apps and cleanup](https://www.notchstar.com/features/disk/): See free space, find big folders, duplicates and app leftovers, compress media and clean caches from your Mac notch. Everything goes to the Trash.
- [How NotchStar finds duplicate files](https://www.notchstar.com/help/find-duplicate-files-notchstar/): Duplicates compares file contents, not names, across six folders. It skips files under 1 MB and hard links, and keeps the oldest copy of each set.
- [How to find the biggest folders on your Mac with NotchStar](https://www.notchstar.com/help/find-biggest-folders-notchstar/): The Space section measures your home folder and ranks folders by size. Click one to look inside, show it in Finder, or move it to the Trash.
- [How to compress large videos with NotchStar](https://www.notchstar.com/help/compress-large-videos-notchstar/): Compress finds photos over 2 MB and videos over 50 MB, recompresses them, and keeps the result only if it is under 90 percent of the original size.

## More in Disk and storage.

- [What the NotchStar Disk scan finds](https://www.notchstar.com/help/what-notchstar-disk-scan-finds/): The Overview scan finds app caches, logs, Xcode build data and downloads untouched for 90 days. It lists them and removes nothing until you choose.
- [Is NotchStar Disk cleanup safe?](https://www.notchstar.com/help/is-notchstar-disk-cleanup-safe/): Disk only moves things to the Trash, only inside your home folder and app bundles in /Applications. It refuses the home folder itself and system paths.
- [How the NotchStar Disk Trash step works](https://www.notchstar.com/help/notchstar-disk-trash-not-permanent-delete/): Disk moves items to the Trash and never deletes for good. Space only comes back when you empty the Trash yourself in Finder.
- [How NotchStar finds duplicate files](https://www.notchstar.com/help/find-duplicate-files-notchstar/): Duplicates compares file contents, not names, across six folders. It skips files under 1 MB and hard links, and keeps the oldest copy of each set.
- [How to remove an app and its leftovers in NotchStar](https://www.notchstar.com/help/remove-app-leftovers-notchstar/): The Apps section lists apps with the caches, preferences and logs they leave in Library. Remove sends the app and those files to the Trash.
- [How to compress large videos with NotchStar](https://www.notchstar.com/help/compress-large-videos-notchstar/): Compress finds photos over 2 MB and videos over 50 MB, recompresses them, and keeps the result only if it is under 90 percent of the original size.