Mac external drive not mounting

When a drive shows in Disk Utility but not in Finder, the Mac can see the disk but the volume on it has not mounted; that is usually repairable. When the drive is missing everywhere, the causes are usually mundane: power, cables and ports. Either way the order matters more than the tool: secure the data first, and only then consider repairs or a reformat.

This guide covers external drives on a Mac: USB, Thunderbolt and SD. It does not cover the Mac's internal drive or boot volumes, FileVault or encrypted volumes whose password is lost, or drives with mechanical symptoms such as clicking; those are different situations with their own routes.

Not sure which situation you are in? Guided help walks you through it.

First, the boring causes

Visible in Disk Utility, missing in Finder

Mounting is the step that connects a volume to the Finder, and it can genuinely fail while the disk itself stays healthy: the diskutil manual describes mounting as a distinct step that can require approval from file system checks before the volume appears. Disk Utility hides part of the picture by default: its sidebar shows only volumes unless you switch to Show All Devices, which is also where Apple says device-level tasks live. Select the greyed-out volume and click Mount; if the volume will not mount on its own, run First Aid on each volume and container in turn, then the device, in that documented order.^[5][6][7]

Read what First Aid reports rather than hoping past it. Apple's wording is blunt in both directions: First Aid can fix formatting and directory errors but cannot detect or repair all problems, and a disk reported as about to fail cannot be repaired at all; the documented instruction is to back up and replace it. If First Aid reports overlapped or unrepairable errors, Apple's own sequence starts with backing up as much data as possible, and only then reformatting.^[7]

The prompts to decline

macOS offers Initialise or Erase in exactly the situations where the volume is unreadable, and Apple uses erase and initialise interchangeably, with a slider for overwriting the erased data. Every one of those buttons deletes the volume's contents; Apple's erase documentation states plainly that erasing deletes everything on the device. The safe answer until your files are copied off is Ignore or Eject, then First Aid, then a recovery scan on a copy where possible.^[1][8]

Formats: what a Mac can read

Some mounting problems are format problems in disguise. A Windows NTFS drive is the classic: Apple documents that Disk Utility does not support NTFS and that a Mac may read from it but never write, so a read-only drive is working, not broken. Apple's own compatibility formats are MS-DOS (FAT) and ExFAT alongside APFS and Mac OS Extended, with GUID Partition Map the scheme for modern Macs. Time Machine has its own preference: Apple names APFS as the preferred backup format and warns that selecting a non-APFS disk prompts to erase and reformat it, which is one of the few prompts worth accepting, but only when the disk holds nothing you need.^{[9][10][11][12]}

Ejecting without losing data

Apple documents ejecting from the Finder before unplugging, and for the disk that refuses to eject because an app is using it, the documented path is to log out and back in, then shut down with the disk connected if needed. Unplugging without ejecting is not a documented safe path; it is simply a risk, and an unnecessary one given the alternative takes seconds.^[13]

When to stop

Stop if the drive makes new noises, does not appear in System Information at all, or if First Aid has declared it failing and the data matters: those are professional cases, and the quotes are cheaper than the attempts. We are an information site, not a recovery provider, and this page makes no claims about third-party Mac recovery software, tested or otherwise; the guidance above rests on Apple's documentation and the drive makers' own support pages.

Clicking hard drive: what to do, and what never to do.

Choosing a data recovery service: quotes, privacy and honest guarantees.