A QDirStat cache file contains directory-tree information collected earlier. Opening that file can be much faster than reading every directory entry again, especially when the original data is remote, slow or very large.
The tradeoff is freshness. A cache represents the filesystem at the time it was generated, so it should be labeled and replaced on a schedule that matches how quickly the underlying data changes.
When cache files are useful
Remote systems
Generate directory data close to the storage, then review it on a workstation without a long interactive network scan.
Scheduled reporting
Create repeat snapshots at known times so storage growth can be compared consistently.
Large stable archives
Avoid rescanning archival trees that change rarely but contain many entries.
Understand cache limitations
Not live data
A deleted, moved or newly created file will not appear correctly until the cache is refreshed.
No direct cleanup guarantee
A cached path may no longer exist or may point to different content by the time you review it. Reconfirm the live path before taking action.
Sensitive metadata
File and directory names can reveal private information even when file contents are absent. Store cache files with suitable permissions.
Build a reliable naming routine
Include the source
Name the cache after the host, mount or directory it describes.
Include a date or sequence
A timestamp helps users understand freshness and prevents accidental replacement of a useful historical snapshot.
Document exclusions
Record whether permission errors or excluded mounts make the cache incomplete.
Refresh at the right frequency
Match change rate
Development folders may need frequent updates, while archives may need only occasional snapshots.
Avoid overlapping jobs
A scheduled cache writer should not start a second run while a previous scan is still active.
Next steps
Return to the main QDirStat page for the source archive, compatibility summary and twenty-question FAQ, or continue with a related guide below.