Drive formats: APFS, Mac OS Extended and exFAT
APFS is the recommended format for a Storage Studio drive. Mac OS Extended also works, exFAT works with warnings, and FAT32 and network drives are refused.
A drive's format decides what it can store besides the files themselves — shortcuts, permissions, access lists and more. Storage Studio relies on those, so it checks the format of any drive you choose and tells you how well it fits.
How each format is treated
| Format | What Storage Studio says | Why |
|---|---|---|
| APFS | Compatibility: looks good | The Mac's own modern format — holds everything a move keeps. Recommended. |
| Mac OS Extended (Journaled) | Compatibility: looks good | The older Mac format; also holds what a move needs. |
| exFAT | Compatibility: usable with warnings | Readable by Windows too, but can't hold several things Macs rely on. |
| MS-DOS (FAT32) | Compatibility: not suitable | Can't hold shortcuts. |
| A network drive | Compatibility: not suitable | Network drives aren't supported. |
| Anything else | Compatibility: usable with warnings | Called non-standard; APFS or Mac OS Extended is recommended. |
The checks appear when you select a drive in Choose External Drive — see Setting up your drive. A drive marked not suitable can't be chosen; for one with warnings, the confirm button reads Use Anyway.
For exFAT, the warning says the format has known issues with macOS shortcuts and permissions, and that APFS is strongly recommended. More in What to know about exFAT drives.
Flowchart outline: How the drive check treats each format
- Drive format
- leads to Which one?
- Which one?
- APFS: leads to Looks good - recommended
- Mac OS Extended: leads to Looks good
- exFAT: leads to Usable with warnings
- FAT32 or network: leads to Not suitable
Case-sensitive formats
APFS and Mac OS Extended both come in a case-sensitive version, where "Photo.jpg" and "photo.jpg" can be two different files. Your Mac's own disk is normally not case-sensitive, where those two names are the same file.
That difference matters when things move back and forth. Before moving an app, the Apps window checks how both your Mac and the drive treat capital letters. If the app contains files whose names differ only in capitals, or if it can't tell how a drive behaves, it refuses the move rather than risk losing a file. Unless you need a case-sensitive drive for a particular reason, the standard, not case-sensitive APFS is the simplest choice.
Changing a drive's format
Formatting is done in macOS's Disk Utility with Erase, and it erases everything on the drive. Copy anything you want to keep somewhere else first. If the drive already holds folders or apps that Storage Studio moved, bring them back to your Mac first — see Moving a folder back — or move them to another drive with Transfer to a New Drive.
See also: APFS, exFAT, Choosing an external drive, What a move keeps.