My external hard drive suddenly stopped showing up in Finder on my Mac, but it contains important files I need to recover. Disk Utility does not seem to mount it. What steps can I safely try without risking data loss?
If macOS cannot detect the physical drive at all, recovery software will not help, so first separate a connection problem from a damaged file system. Stop reconnecting it repeatedly if it clicks, beeps, spins down, or disconnects. Do not erase, initialize, partition, or reformat it, even if macOS prompts you.
Try another known-good cable and port, connect directly rather than through a hub, and test the drive on another computer. Apple specifically recommends a direct connection when power or recognition is an issue. In Disk Utility, choose View > Show All Devices because the default view can hide the physical device while showing only volumes. You can also run diskutil list in Terminal. If the drive appears there with roughly the correct capacity, there is a reasonable chance of software recovery even if it will not mount.
For important files, I would image or clone the drive to a healthy disk before attempting repairs. First Aid changes file-system structures, so repeatedly running it on an unstable drive is not the safest first move, even though Apple recommends it for repairable directory errors. A tool such as Disk Drill for Mac can scan the detected drive or, preferably, its image. Recover files to a different disk, never back onto the failing one. If the physical device does not appear in Disk Utility or diskutil list with multiple cables and computers, or it makes unusual noises, power it off and use a professional recovery lab.
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A portable drive that powers on but will not mount is a different problem from a desktop external drive whose enclosure or power adapter has failed. @ellie’s cable and port checks are sensible, but people often overlook the enclosure electronics. For a 3.5-inch drive, test a compatible power supply if one is available. For a removable SATA drive, a different known-good enclosure or SATA-to-USB adapter may reveal that the disk itself is fine. Do not open sealed units or swap hardware if the enclosure provides encryption, since some models need their original USB bridge to decode the data.
If the disk appears with the correct capacity but the volume stays greyed out, avoid repair attempts until the important files are copied. Try mounting it once, and if that fails, scan the disk or an image of it with recovery software. Save recovered files to another drive. A read-only scan is preferable to repeated First Aid runs because repairs can make a damaged directory worse.
If it keeps disappearing, reports the wrong size, becomes extremely slow, or makes mechanical noises, stop testing. At that point, even creating an image can stress a failing drive, and professional recovery is the lower-risk option for irreplaceable files.
Do not erase, initialize, partition, or reformat the drive when macOS offers to “fix” it. Those actions can overwrite the file-system information recovery tools need.
First, open Disk Utility and choose View > Show All Devices. If the physical disk appears, note whether its capacity looks correct and whether an encrypted APFS volume simply needs to be unlocked. If it does not appear there, check System Information under USB or Thunderbolt. This separates a Finder or volume problem from a connection or hardware problem. Trying the drive on another Mac can provide the same clue, but decline any repair or initialization prompts.
If the disk appears reliably with the correct size, scan it without writing changes. Disk Drill for Mac is an option, but recover the files to a different disk, never back onto the problem drive. I would skip repeated mount attempts and First Aid until the important data is copied. If the drive disconnects during a scan, stalls for long periods, or makes clicking sounds, stop. At that point DIY software is more likely to reduce the remaining recovery window than save money.
If the drive is an SSD and not a spinning disk, treat the timeline as much tighter. When an SSD controller starts failing, it often goes from readable to completely dead with no warning, and imaging attempts frequently stall or return garbage because the controller itself is the broken part. The clone-first advice everyone is giving is solid for a normal hard drive, but on a dying SSD you sometimes get one good read window and that’s it.
The imaging step keeps coming up here without anyone saying how to actually do it, so: for a spinning drive that reads but errors out, ddrescue is free and built for exactly this. It skips bad sectors, keeps a map file, and lets you resume instead of hammering the same bad spot over and over the way a plain copy does. Once you have the image, you point recovery software at that file and leave the physical drive powered off. That way Disk Drill or whatever you use is scanning a static copy, not stressing the original. @ellie and @0xcoder9 are right that scanning the image beats scanning the live drive, I’d just add that a normal drag-copy is not the tool for a flaky disk.
One thing worth checking before any of this: bus-powered 2.5 inch drives sometimes vanish simply because a port or hub can’t supply enough current. Same drive on a powered hub or a rear port on a desktop Mac can come back like nothing was wrong. Cheap to rule out, and it happens more than people expect. If it clicks or the capacity reads wrong though, skip the DIY route entirely and budget for a lab.