I've just had some problems with a disk that was formatted with HFS+ case sensitive while every else by Apple was non case sensitive.

After a long time moving things away from my biggest disk, partitioning and formatting non-case-sensitive, I've found out that Time Machine does format "case sensitive"

Why Apple wants case-sensitive only for Time Machine??? What's the technical advantage? I've just invested a long time fixing sync problems with my disks because of different case sensitivity problems

3 Answers 3


Case-sensitive and -insensitive filesystems under OS X are a mess (to say the least), primarily because some well-known and big software companies require their software to be installed on an case-insensitive filesystem. Otherwise these applications wouldn't really work because accessing IMPORTANT-RESOURCE.jpg would never work with a file named important-resource.jpg on disk.

On the other hand, for Time Machine backups, this is not really important because you will never run an application directly from your Time Machine drive. Using a case sensitive filesystem, in that case, covers both possible options without negative impact.

  • 2
    Indeed - if the system allows you to make drives that are case-sensitive, the Time Machine destination has to be case sensitive to back those drives up and changing case in mid-stream would be very disruptive or perhaps impossible.
    – bmike
    Sep 12, 2014 at 20:19

A case sensitive file system is guaranteed compatible to store data from another case sensitive and case insensitive file system. Apple chose case sensitivity for Time Machine, so that it can incorporate backups from both types of file systems.

Example: - Suppose you have a case sensitive file system, which has FILE1 and file1. You cannot copy those files side by side to a case insensitive file system, as the latter would see those files as one and the same file. - Suppose you have a case insensitive file system: you cannot create FILE1 and file1 side by side. So you can copy all your files to a case sensitive file system.

That is a good choice unless you do not want third party applications to find their files as they might not find them if typed incorrectly (wrong case).

  • I always thought any *nix-based system like OS X would be case-sensitive, although (just tested to make sure!) on Big Sur I cannot create 'FILE1' and 'file1' in the same folder, so it appears case-insensitive. However, after it has formatted my backup drive, Time Machine only has a "case sensitive" option. Nov 23, 2021 at 12:34
  • Windows and Mac-based file systems have always seemed to me to have a more human approach to file systems. Not having to worry about case makes the computer simply much easier to use, especially for newer users. Mar 23, 2023 at 6:23

While this does not answer your question as to why this may solve your problem in the future.


  • 1
    Answers on Ask Different need to be more than just a link. We expect answers to be self contained, since if your link goes down, your answer will be useless. Paraphrasing the source and including any relevant information in the answer will ensure it stays relevant
    – nohillside
    Feb 27, 2022 at 16:40

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