Analyze External Drive Space on Mac
When a drive opens normally but is almost full, compare its folders to identify the largest projects. Confirm the selected drive before following the largest branches.
An external drive holding video, work projects, or archives can gradually fill up. If it opens normally, compare the folders to learn whether source media, exports, or old projects account for the usage.
DiskTreeSize analyzes the accessible folder you select. Choose a location on the external drive explicitly, and keep the folder results separate from the drive's overall capacity.
Confirm the drive opens in Finder
Connect the drive, locate it in Finder's sidebar, and open a known folder. If the device is absent, locked, or unreadable, address that first. Folder analysis does not repair an inaccessible disk.
Apple's external storage guide explains connections, access, and ejection. Keep the device connected while scanning and saving a report, then eject it normally.
Select a location on that drive
- Click Choose Location in DiskTreeSize.
- Select a drive folder such as Media or Project Archives. To compare top-level folders, you can select the drive root if accessible.
- Confirm the location and start Analyze. Wait for completion.
- Check the tree's root path so you do not confuse it with a similarly named folder on the internal disk.
By default, a scan stays on its current volume. An internal drive scan does not automatically include every attached device; select the external location separately.
Trace projects into media and exports
Sort Size or Allocated from largest to smallest. Expand the largest project and distinguish source media, exports, and archive files.
For a large editing project, identify its components instead of assuming the whole folder is disposable. The folder-size guide covers the controls.
File Types summarizes the overall scan by extension and can show whether video or archives account for substantial usage. It does not summarize only the selected subfolder or determine whether media is still needed.
Interpret three different numbers
| Number | Scope | Use it for |
|---|---|---|
| Folder size in the tree | Items scanned beneath that folder | Comparing projects and following branches |
| Percentage of parent | The item's share of its parent folder | Comparing siblings, not the whole drive |
| Available / total in the status bar | Capacity reported by the location's volume | Checking the drive, not the selected folder's capacity |
Selecting Media excludes other drive folders from the tree's total. Skipped files and file system measurements can also affect comparisons; see allocated and logical size.
Reading and organizing have different requirements
Scanning, sorting, and Copy Path are free. Pro is optional paid access, or an active trial, for Finder navigation, report export, and confirmed moves to Trash.
Being able to read a directory does not guarantee write access. Move to Trash depends on drive and file permissions and cannot target the scan root. You can save a report to a writable location on the Mac if the drive does not permit writing.
Before relocating an old project, check the destination's capacity and verify the copied contents before deciding what to do with the originals. DiskTreeSize analyzes usage; it does not automatically relocate or merge projects.
Keep comparable results
Rescan the same folder after organizing it. If you need a record, export before-and-after CSV files for a spreadsheet and note the drive name, scan location, and dates. The report export guide explains the scope and limits.
Check actual available drive space afterward. Removing an item from the displayed tree does not guarantee an immediate matching increase in free capacity.
Frequently asked questions
Can DiskTreeSize analyze folders on an external drive?
You can select a connected, accessible drive folder for analysis. The scan still depends on macOS access permissions and the chosen scope. Resolve connection or access problems first if the drive cannot be opened.
Why wasn't my external drive included in an internal drive scan?
By default, scanning stays on the current volume. Selecting an internal location does not automatically analyze other attached drives. Use Choose Location to select the external drive folder separately.
Does read access guarantee Move to Trash will work?
No. File actions also depend on write access and require Pro or an active trial. Wait for scanning to finish and select a child item; the scan root cannot be moved to Trash.
