The disk you attached was not readable by this computer: what not to click
macOS offers Initialize, Ignore or Eject. Initialize erases the drive. Why the Mac cannot read it, how to find out, and how to keep the data if it matters.
You plug a drive in and macOS says The disk you attached was not readable by this computer, with three buttons: Initialize, Ignore and Eject. Initialize erases the drive. If there is anything on it you need, click Ignore or Eject.
Why a Mac cannot read a drive
| Cause | How to tell |
|---|---|
| Formatted for Linux, such as ext4 | It came from a Linux machine, a Raspberry Pi or some NAS boxes |
| Encrypted with BitLocker | It came from a Windows PC with encryption on |
| Brand new and never formatted | Nothing has ever been on it |
| Damaged file system or partition table | It worked before, and was unplugged without ejecting |
| Failing drive | Clicking, slow to appear, disconnects |
diskutil list external
diskutil info /dev/disk4 # use the disk number from the listThe partition type in that output often names the format, such as Linux Filesystem or Microsoft Basic Data.
What to do for each
- Brand new: Initialize is what you want. Choose a format as in formatting for Mac and Windows.
- Linux or BitLocker: read it on the computer it came from and copy the data off, or use a tool made for that format.
- Damaged file system: open Disk Utility, select the volume and run First Aid. If that fails, see First Aid failed.
- Failing drive: stop using it. Every attempt can make recovery harder. A professional recovery service is the safe route for irreplaceable data.
Common questions
What does the disk you attached was not readable by this computer mean?
macOS does not recognise the drive's format, or the format is damaged. It may be formatted for Linux, encrypted with BitLocker, brand new, or failing.
Will Initialize erase my external drive?
Yes. Initialize opens Disk Utility to erase and format the drive. Click Ignore or Eject if you need the data.
How do I recover data from an unreadable drive on a Mac?
Read it on the computer it came from if it is Linux or BitLocker formatted. If it is damaged, try First Aid. If it is failing, stop using it and consider a recovery service.