An external hard drive that doesn't show up on your Mac is usually one of five things: Finder is hiding it, the cable or port isn't delivering data or power, the drive isn't mounted, the format isn't readable, or the drive itself has failed. The first three take under two minutes to check and cover most cases. Work through the steps in order; each one tells you what its result means for the next step.
TL;DR: Check Finder settings first (external disks hidden is the most common non-problem), then try another cable and port. If Disk Utility sees the drive but it isn't mounted, click Mount, then run First Aid. If Disk Utility doesn't see it at all, check System Information → USB. A drive that clicks, or appears and disappears, is failing: stop and get the data off first.
First: Is the Drive Actually Missing, or Just Hidden?
Finder hides external drives by default on some setups, and this "fix" resolves an embarrassing share of cases. Open Finder, then Finder → Settings → General, and check External disks under "Show these items on the desktop." Then Settings → Sidebar, and check External disks under Locations.
If the drive was mounted all along, it now appears. If not, keep going.
Check the Cable, Port, and Power
Unplug the drive and try, in order: a different port on your Mac, a different cable, and plugging directly into the Mac instead of through a hub or monitor.
Cables fail more often than drives do, and charge-only USB-C cables (the kind that ship with some accessories) carry power but no data. Desktop 3.5-inch drives have their own power supply; confirm its light is on. Portable 2.5-inch drives draw power from the port, and an unpowered hub often can't deliver enough, especially with several devices attached.
If the drive spins up (you can feel a faint vibration) but never appears, move on to Disk Utility. If it's completely dead (no vibration, no light), the enclosure's power or the drive itself is the problem.
Check Disk Utility, and Click "Show All Devices"
Open Disk Utility (Applications → Utilities). First, go to View → Show All Devices in the menu bar. Without this, Disk Utility hides the physical drive and only shows volumes, which is exactly the wrong view for diagnosing a drive that won't mount.
Now look at the sidebar:
The drive appears with a volume grayed out underneath. The Mac sees the hardware; the volume just isn't mounted. Select the grayed volume and click Mount. If it mounts, you're done. If macOS refuses with an error, run First Aid (next step).
The physical drive appears but shows no volume at all. The partition map or filesystem is damaged, or the drive was never formatted. If there's data on it you care about, do not click Erase. Skip to the recovery section.
The drive doesn't appear at all, even with Show All Devices on. Check whether the Mac sees it at the USB level: Apple menu → About This Mac → More Info → System Report → USB (or SPI/Thunderbolt, depending on connection). If the drive is listed there but not in Disk Utility, the drive's controller is responding but the disk isn't. That usually means hardware failure. If it's not listed in the System Report either, the Mac genuinely isn't seeing the device: cable, port, enclosure, or dead drive.
Run First Aid
With the drive or volume selected in Disk Utility, click First Aid. Run it on the volume first, then on the physical device. First Aid repairs directory structures and filesystem errors, which are the usual reason a volume mounts on one computer but not another, or stopped mounting after an unsafe eject.
If First Aid fails with "the underlying task reported failure," run it a second time. If it fails repeatedly, the filesystem is damaged beyond what macOS can repair in place. That's recoverable with third-party tools, but stop writing anything to the drive.
Try Mounting From the Terminal
The terminal gives you more detail than Disk Utility when things get stubborn. List every disk the Mac can see:
diskutil list external
You'll get output like /dev/disk4 (external, physical) with its partitions listed underneath. Try mounting the whole disk:
diskutil mountDisk /dev/disk4
If mounting fails, the error message here is more specific than Disk Utility's, and worth searching verbatim. A common one on exFAT drives after an unsafe eject is a dirty filesystem flag; macOS runs fsck_exfat automatically on mount attempts, and you can watch whether that check is what's hanging by trying the mount and waiting a minute or two before judging the result.
Is the Drive Format the Problem?
macOS reads and writes APFS, Mac OS Extended (HFS+), exFAT, and FAT32. It reads NTFS (the Windows default) but does not write to it, and some NTFS drives with errors won't mount at all. A drive formatted as ext4 (Linux) or as a Windows Storage Space won't appear as a usable volume no matter what you do, even though Disk Utility sees the hardware.
If the drive came from a Windows machine and holds data you need, read it on a Windows machine, copy the data off, then reformat it as exFAT (works on both platforms) or APFS (Mac only). The external drive guide covers which format fits which use.
Signs the Drive Is Failing (Stop and Act)
Any of these means the drive's hardware is dying, and every additional minute of use reduces what's recoverable:
- Clicking, beeping, or grinding sounds
- The drive mounts, then disappears, then reappears
- Finder freezes whenever the drive connects
- Files open extremely slowly or copies fail partway
Stop running First Aid, stop remounting it repeatedly, and copy the most important data off first, starting with the files that exist nowhere else. If the drive won't stay mounted long enough to copy anything and the data matters (a client project, family photos), a professional recovery service is the honest answer. Software can't fix physically failing hardware, and DIY attempts on a mechanically failing drive make professional recovery harder.
The Question After the Rescue: What Was on That Drive?
When a drive dies or comes back blank, the immediate panic is the files. The lasting problem is that most people can't say what was on it. Which shoots, which projects, which of them existed only there.
Tusk is a Mac app that automatically backs up your project folders to multiple locations and tracks where every file lives — even when your drives aren't connected.
This is the exact problem Tusk exists for. It tracks every file in your projects across all your drives by checksum, and it keeps that index even when drives are unplugged. When a drive fails, you can see precisely which files lived there and which of them have verified copies on other destinations, so "did I lose anything?" gets a real answer instead of a guess. And its restore flow rebuilds the lost drive's contents from your other copies in one action.
If you just need a quick inventory of drives that still work, our free disk cataloging tool scans any mounted drive in the browser and exports a CSV file list. Nothing gets uploaded. It's a one-time snapshot rather than ongoing tracking, but it means the next dead drive comes with a manifest. For the full workflow, the guide on tracking files across external drives covers how creators keep multi-drive setups accounted for.
FAQ
In rough order of likelihood: Finder is set to hide external disks (check Finder → Settings → General and Sidebar), the cable or port isn't delivering data (charge-only USB-C cables are a common trap), the volume isn't mounted (open Disk Utility, enable View → Show All Devices, and click Mount), the drive's format isn't readable by macOS (NTFS is read-only, ext4 unsupported), or the drive is failing. Working through those checks in order isolates the cause in a few minutes.
Select the volume and click Mount. If macOS refuses, run First Aid on the volume and then on the physical device; filesystem damage after an unsafe eject is the usual cause and First Aid often repairs it. If First Aid fails repeatedly, try mounting from the terminal with diskutil mountDisk to get a more specific error. Stop short of erasing the drive if it holds data you need.
The same fixes apply regardless of brand: Finder visibility settings, cable and power, mount status in Disk Utility, format, and drive health. Two brand-specific notes: desktop-size Seagate and WD drives need their own power adapter connected and working, and some pre-formatted drives ship as NTFS, which macOS can read but not write. Reformatting to exFAT or APFS (after copying data off) fixes the format issue.
Almost always because it's formatted as NTFS, the Windows default, which macOS reads but doesn't write to. Copy the data somewhere safe, then reformat the drive in Disk Utility as exFAT if you need it to work with both Windows and Mac, or APFS if it's Mac-only. Occasionally read-only status comes from permissions instead: select the drive in Finder, press Cmd+I, and check the Sharing & Permissions section.
Often, yes. If the drive is mechanically healthy and only the filesystem is damaged, recovery software can usually read the raw disk and extract files. If the drive is making clicking or grinding noises, or keeps disconnecting, that's hardware failure: stop using it and weigh professional recovery against the value of the data. Either way, copy off the files that exist nowhere else first, and treat the incident as the argument for keeping verified copies of anything important on at least two destinations going forward.