“The disk you inserted was not readable by this computer”: click Ignore, not Initialize

This message means macOS can see the drive but can’t make sense of its contents. Click Ignore. Don’t click Initialize, which erases the drive. Your files are often still there, and you can usually copy them off before fixing anything.

By Jishnu Mahanta · Updated 2026-10-20

In short

Click Ignore. Then check whether the drive shows in Disk Utility (View > Show All Devices). Don’t Initialize, Erase or run repairs yet. Read the drive with a read-only tool, copy your files to another drive, verify the copy, and only then repair or reformat.

What the three buttons do

On current macOS (Sequoia and Tahoe) the dialog reads “The disk you attached was not readable by this computer”; older versions say “inserted”. It offers three buttons:

Ignore closes the dialog and changes nothing on the drive. This is the one you want.
Eject safely disconnects the drive. Fine, but you will have to plug it in again to carry on.
Initialize… opens Disk Utility’s erase screen. Going through with it creates a new, empty file system. It writes to the drive and erases what you had.

One exception: if the drive is brand new, or you know it has nothing on it, Initialize is exactly right. Everything below is for drives that hold files you want.

Why macOS says it isn’t readable

The message appears when the Mac can’t mount the drive’s file system. Common reasons:

The drive was unplugged or lost power without ejecting, so the file system was left in an inconsistent state.
The partition map or file system is damaged.
The file system is one macOS can’t read at all, such as ext4 (Linux and Raspberry Pi), a BitLocker-encrypted Windows drive, or a RAW partition on a drive Windows has lost track of.
An SD card or USB stick that failed, or a cable, port or enclosure fault that makes the data unreadable even though the device is detected.

There’s no official Apple page that lists these causes for this exact message, so treat the list as the usual suspects, not a diagnosis. The checks below tell you which one you have.

Safe checks that only look

Click Ignore. Then try a different cable and a different port, plugged straight into the Mac, not a hub. Bus-powered spinning drives sometimes need the drive’s own power supply.
Open Disk Utility (Applications > Utilities) and choose View > Show All Devices. If the physical drive appears in the sidebar, the Mac can talk to it and the problem is the contents. Selecting it is harmless.
In Terminal run diskutil list. This only reads and prints every disk macOS knows. Look for your drive by its size. A partition type such as Linux Filesystem, Microsoft Basic Data or no type at all tells you what you’re dealing with.
Run diskutil info disk4 (use your own disk number) to see the file system, size and whether macOS thinks it is a removable device. Also read-only.
Check System Information. Hold Option and choose Apple menu > System Information, then look under USB, Thunderbolt or Storage. If the drive isn’t listed there or in diskutil list, macOS can’t even see the device: that is a connection or hardware problem, not a file system problem. See External hard drive not showing up on Mac.

The one step that writes: First Aid

Apple’s guidance is to run First Aid on each volume, then the container, then the whole device (Apple: Repair a storage device with Disk Utility). It can fix a lot, and Apple also warns it can’t repair everything. First Aid writes to the drive. On a healthy drive with minor corruption that is usually fine. On a drive that is failing, or holds files you can’t replace, copy first. If First Aid has already failed for you, see Disk Utility First Aid failed (exit code 8).

Copy your files off with Retrova

Retrova understands APFS, Mac OS Extended (HFS+), NTFS, FAT12/16/32, exFAT, ext2/3/4, XFS and Btrfs, finds partitions on GPT and MBR disks, and opens the drive read-only. It doesn’t mount, repair or format anything. If the drive is encrypted (BitLocker, LUKS or FileVault), Retrova marks it Locked and opens it when you enter the password or recovery key.

Plug the drive in and open Retrova. On the home screen choose A drive won’t open. Retrova lists every drive and partition it can see, with the file system it detected.
Pick the drive or partition. macOS asks for your administrator password at this point, because reading a disk directly needs it. Retrova only uses it to read.
Browse and choose what you want back. If the file system is readable you see your original folders and file names, and you can preview photos, videos, PDFs and text before copying.
Choose a destination on a different drive with enough free space. Retrova never saves onto the drive it is reading.
Copy, then Verify. Files are written as temporary parts and renamed only when complete. When it finishes, run Verify to compare every copy with the original, byte for byte.

If no file system is recognised, or the one it finds is too damaged to list files, run Deep scan from I deleted something. Deep scan ignores the file system and searches the raw drive for the start of 72 known file types (photos including camera RAW, videos, audio, documents, archives, mail files and more). It only recovers files that were stored in one piece, and the original names and folders are lost: finds come back sorted by type with new names.

What Retrova can’t do: it can’t undelete files with their names on APFS, ext or other file systems (only NTFS, FAT and exFAT), can’t open an encrypted drive without its password or recovery key, can’t open the startup disk of a T2 or Apple silicon Mac away from that Mac, doesn’t handle RAID sets or phones, and can’t fix a drive with physical damage. Retrova’s builds aren’t signed or notarised yet, so macOS and Windows will show a warning the first time you open it.

If the drive is also slow, disconnecting or making noise, make an image first: Image a failing drive on Mac or Windows.

What not to do

What not to do

Don’t click Initialize or Erase. They create a new empty file system.
Don’t keep running First Aid on a drive that might be failing. Each attempt is more wear.
Don’t save anything onto the drive, including “recovered” files.
Don’t keep unplugging and re-plugging a drive that clicks or disconnects. Power it down.

Get Retrova

Free and open source for macOS 11+ and Windows 10/11. No account, no recovery limit, and it never writes to the drive you’re rescuing.

Download RetrovaFree for Mac and Windows

Questions

Should I click Ignore, Eject or Initialize?

Click Ignore. It closes the message and changes nothing. Initialize erases the drive and creates an empty file system, so only use it on a drive that is new or has nothing you need.

Is my data gone if the disk is not readable?

Usually not. The message means macOS couldn’t mount the file system, not that your files were erased. Whether they can be recovered depends on whether the drive is physically healthy and hasn’t been overwritten.

Does Retrova fix the drive?

No. It never repairs or formats the source. It reads the drive and copies your files elsewhere. Repair or reformat only after your files are safe.

The drive does not appear in Disk Utility at all. What now?

If it is missing from Disk Utility with Show All Devices on, from diskutil list and from System Information, the Mac can’t see the device. Try another cable, port and computer. If it still doesn’t appear anywhere, the hardware has failed and software can’t help; a professional recovery lab is the next step.

Sources

Apple: Repair a Mac storage device with Disk Utility