External drive not mounting on macOS 26 Tahoe: what to check

Is it Tahoe, or the drive?

I can’t point you to an Apple-confirmed bug that stops external drives mounting on macOS 26 Tahoe, and I won’t guess at one. What I can say is that the causes are the same ones as on macOS 15 Sequoia: permissions, settings, the connection, or a damaged file system. The quickest way to separate “Tahoe” from “the drive” is to try the drive on another Mac or a Windows PC. If it behaves the same elsewhere, the drive is the problem.

Checks that only look

1. Accessory permission (Mac laptops with Apple silicon). Apple’s setting is in System Settings > Privacy & Security > Allow accessories to connect. When you plug in a new USB or Thunderbolt accessory, or an SD card, you should get an alert asking you to allow it. If you chose Don’t Allow, or the Mac was locked, the drive won’t be exposed. Unlock the Mac, unplug, plug in again and choose Allow (Apple).
2. Finder settings. In Finder choose Finder > Settings. Under General, tick External disks to show them on the desktop, and under Sidebar tick External disks. A drive that is mounted but hidden is the most common “not showing up”.
3. Disk Utility. Open it, choose View > Show All Devices. The drive in the sidebar means the Mac sees it. If its volume is greyed out, it is detected but not mounted. Click Mount; if that gives an error, see “Could not mount”: com.apple.DiskManagement.disenter error.
4. Terminal, read-only: diskutil list prints every disk, and diskutil info disk4 describes one (use your number).
5. Cable, port, power. Use another cable and a port directly on the Mac, not a hub. A spinning drive may need its own power supply.
6. Restart with the drive unplugged, then plug it in. If it was disconnected without ejecting, macOS may be running a check on it; give it a few minutes.
7. Check the format. macOS mounts APFS, Mac OS Extended, exFAT, FAT32 and NTFS (read-only). It can’t mount ext4 (Linux/Raspberry Pi) or BitLocker-encrypted drives. “Not readable” for those is expected, not damage.

If the drive doesn’t appear anywhere, in Disk Utility with Show All Devices on, in diskutil list or in System Information (hold Option, Apple menu > System Information > USB or Thunderbolt), see External hard drive not showing up on Mac.

One step that writes

Disk Utility’s First Aid is the standard repair, and Apple documents running it on volume, container then device (Apple). It writes to the drive, so if the files matter, copy first. If it fails, see Disk Utility First Aid failed (exit code 8).

Copy your files off with Retrova

If the drive is detected but won’t mount, or macOS says it can’t read it, Retrova can usually still read the file system directly, read-only. It supports APFS, Mac OS Extended (HFS+), exFAT, FAT, NTFS, ext2/3/4, XFS and Btrfs.

1. 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.
2. 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.
3. 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.
4. Choose a destination on a different drive with enough free space. Retrova never saves onto the drive it is reading.
5. 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.

Retrova is built for macOS 11 and later and isn’t yet signed or notarised, so expect a first-launch warning from macOS.

What not to do

Questions

Sources

• Apple: Allow USB and other accessories to connect to your Mac
• Apple: Repair a Mac storage device with Disk Utility

Related guides

• External hard drive not showing up on MacNot detected or not mounted? Two different problems.
• “Could not mount”: com.apple.DiskManagement.disenter errorErrors 0, 49153 and 49218: gentle steps, then a read-only copy.
• External drive not mounting on a Mac? Get your files off it firstmacOS sees the drive but it will not open? The safe order of things.
• Copy files from an NTFS drive on a MacRead an NTFS drive on macOS without a paid driver.