My external hard drive suddenly stopped mounting on my Mac, even though it still shows up in Disk Utility. I’ve tried unplugging it, restarting my Mac, and running First Aid, but I still can’t access my files. I need help figuring out what’s causing this and how to safely get the drive to mount again without losing data.
I hit this on my Mac a while back. Plugged in an external drive, got power, got noise, got nothing on screen. No Finder icon. No mount. It felt bad for about ten minutes, then it turned out to be fixable.
Start with the dumb stuff first, because the dumb stuff gets missed.
Plug the drive straight into the Mac. If you’re using a hub, remove it. Older hard drives, the spinning kind, often act weird when the hub feeds weak power. Swap the cable too. Swap the port. I once burned half an evening on a “dead” SSD and the problem was the USB-C cable. Looked fine. Wasn’t fine.
If the drive has a light, check it. If it spins or vibrates, I’d take that as a decent sign. Power is reaching it. Dead-silent hardware is a worse story.
Next thing, check whether macOS is hiding it instead of failing to mount it.
Open Finder, then Settings. On older macOS versions it says Preferences. In General, make sure External disks is enabled. Then open Sidebar and check External disks there too. I know, this sounds too small to matter. It does matter. I’ve seen mounted drives stay invisible because of one unchecked box.
If Finder still shows nothing, open Disk Utility.
Before you hit any repair button, pause. If the files on the drive matter, don’t go clicking First Aid or Erase on impulse. I’ve watched people turn a recoverable mess into a clean empty disk. If the drive appears in Disk Utility but refuses to mount, I’d suspect file system damage, not instant hardware death.
My move at this point is data recovery first. Repair later. macOS tends to reject a disk fast if the file system looks off. Recovery tools don’t rely on the same mount process. They read the drive more directly and often pull files even when Finder refuses to deal with it.
I’ve had the best results here with Disk Drill. It’s one of the few tools I’ve used on unmounted and damaged drives where the scan wasn’t a total waste of time. On a good run, you’ll see the old folder tree, file names, and enough preview data to check whether recovery looks clean. The byte-to-byte backup option matters too. If the drive is unstable, make an image first and scan the image instead of hammering the physical disk. Safer move. Less wear. Better odds if the hardware is fading out.
Once your files are copied off, then mess with repairs.
If your data is already safe, or you don’t care about the contents, these are the next things I’d try:
Open Terminal and run sudo pkill -f fsck. This sounds random, but it isn’t. After an unsafe unplug, macOS sometimes starts fsck in the background to inspect the disk. I’ve seen fsck hang and block mounting for a long time. Kill it, and the drive sometimes appears right away. Weird, but I’ve seen it work.
If you’re on an Intel Mac, reset NVRAM or SMC. USB behavior and low-level hardware settings sometimes get stuck in ugly ways. On Apple Silicon systems, a restart handles most of what those resets used to cover.
Last step, reformat the drive. In Disk Utility, choose View, then Show All Devices. Select the physical disk, not only the volume underneath it, then click Erase. Pick APFS if the drive stays in the Mac ecosystem. Pick exFAT if you move files between macOS and Windows. This wipes the disk and builds a fresh file system. If mounting still fails after a clean format, I’d start assuming the hardware itself is going bad.
The order matters. Get the files first. Repair second. Drives fail. Cables fail. Enclosures fail. Your data doesn’t get a retry if you wipe it by accident. If you need the contents, pull them off with Disk Drill before doing anything destructive.
4 Likes
If Disk Utility sees the drive, your Mac still detects the hardware. The fail point is often the volume, mount process, enclosure, or file system driver.
A few things I’d check that @mikeappsreviewer didn’t get into much:
-
Look at the exact status in Disk Utility.
If the physical disk appears, but the volume under it is gray or unmounted, click the volume and check the format listed on the right. If it says NTFS, macOS reads it but won’t write to it, and a dirty NTFS volume from Windows often refuses to mount at all until Windows repairs it with chkdsk. I see this a lot with cross-platform drives. -
Try mounting from Terminal.
Open Terminal and run:
diskutil list
Find your external volume identifier, like disk2s1, then run:
diskutil mount /dev/disk2s1
If it throws an error, the wording matters. “Resource busy” points one way. “Incorrect file system” points another. “Could not mount” with I/O errors points toward hardware or enclosure trouble. -
Check system logs.
Run:
log stream --predicate ‘eventMessage contains ‘disk’’ --info
Then plug the drive in again. If you see repeated I/O errors, disconnects, or bridge resets, the enclosure board is suspect. I’ve seen plenty of “dead drives” where the SATA-to-USB bridge was the real problem. -
If it’s a desktop external, test the bare drive in another enclosure or dock.
This matters a lot for 3.5-inch externals. The disk inside is often fine. The cheap USB board dies first. Easy thing to miss. -
If the drive was encrypted, verify unlock state.
APFS or HFS+ encrypted volumes show up in Disk Utility but stay unavailable until unlocked. In Terminal:
diskutil apfs list
Look for a locked volume or encrypted container.
I mildly disagree with killing fsck early. If the drive is making odd noises or dropping offline, every extra write or retry is risk. At that point I’d switch to recovery first. Disk Drill is a solid pick for pulling files from a volume macOS won’t mount, espeically if Finder is useless but the disk still enumerates.
If you want a step-by-step video version, this one is decent:
watch the Mac external drive not mounting fix guide
If you post the output of diskutil list and the exact error from Terminal mount, people here can narrow it down fast.
If Disk Utility sees the device but won’t mount the volume, I’d also check one thing people skip: whether the partition map itself is damaged, not just the file system. In Disk Utility, click View > Show All Devices and see if the top-level disk looks normal but the volume beneath it is missing weirdly or shows the wrong size. That can happen after unsafe ejects or flaky enclosures.
I’d also test it in Safe Mode. Not because Safe Mode is magic, but because third-party filesystem stuff, antivirus, cleanup apps, and old NTFS drivers can interfere with mounting. Seen that more than once, actualy.
One small disagreement with @mikeappsreviewer and @voyageurdubois: I would not keep rerunning First Aid over and over if the drive has important data. One pass, fine. Repeated repair attempts on a sick drive can make a bad day worse. If the files matter, switch priorities to recovery. Disk Drill is a reasonable option here because it can scan a drive Mac can still detect even when Finder won’t mount it.
Also try another Mac if you can. If it fails the same way on two systems, that points back to the drive/enclosure, not your OS.
If the drive mounts read-only anywhere, copy data off immediatley and stop testing.
For extra reading, this is pretty relevant: best fixes for an external hard drive not mounting on Mac