---
id: apps.what-does-files-that-differ-only-by-case-mean
url: https://storagestudio.us/faq/apps/what-does-files-that-differ-only-by-case-mean
category: "Apps"
subcategory: "Drive, safety and recovery"
question: "Why does an app move fail with \"files that differ only by case\"?"
alt_questions:
  - "Case-sensitive drive app move error"
  - "Files would collide on the destination"
  - "Reformat drive as case-insensitive APFS"
  - "App won't move to case-sensitive drive"
short_answer: "Your fast drive is case-sensitive and the app has files whose names differ only by capitals, so they'd clash. Nothing is changed; a standard (case-insensitive) APFS drive avoids it."
tags: ["error", "drive format", "case-sensitive"]
related: ["https://storagestudio.us/faq/apps/why-did-an-app-move-fail"]
applies_to: "all"
last_reviewed: 2026-10-01
---

# Why does an app move fail with "files that differ only by case"?

Your fast drive is formatted as **case-sensitive** while your Mac's built-in drive isn't, and this app contains files whose names differ only by capital letters. On the built-in drive they're treated one way, on the external drive another, so they would clash — and Storage Studio stops rather than risk a broken copy.

Nothing is changed. Most people never see this; if you do, the reliable fix is to use a drive formatted as standard (case-insensitive) APFS. See [external drives](https://storagestudio.us/faq/external-drives/).