External drives are the cheapest storage you can buy and the most common source of "it's not working." Almost every problem falls into one of four categories: the wrong connector, the wrong format, insufficient power, or a failing drive.
Here's how to tell which.
Connectors, decoded
The naming in this area is genuinely bad, and it's not your fault if it's confusing.
USB-A — the familiar rectangular connector. Only goes in one way. Still on most computers.
USB-C — the small oval, reversible. The current standard, and the one that causes the most confusion because the connector shape tells you nothing about the speed. A USB-C cable might carry data at older, slower speeds or at very fast modern ones, and they look identical.
Thunderbolt — uses the USB-C connector shape, marked with a lightning bolt. Much faster, and more expensive. A Thunderbolt port accepts USB-C devices; a plain USB-C port doesn't provide Thunderbolt speeds.
Micro-USB and Mini-USB — older, on older drives.
The practical implications:
The cable matters as much as the ports. A slow cable between two fast ports gives you slow transfers. If a drive is unexpectedly slow, try the cable that came with it before assuming the drive is faulty.
Check your ports before buying. A drive with a connector your machine doesn't have needs an adapter, and adapters are where reliability problems start.
Buy a drive with a detachable cable where you can. Cables fail far more often than drives, and a captive cable failure makes the drive scrap.
Why a drive doesn't show up
Work through these in order.
1. Try a different cable. The most common cause by a wide margin, and the easiest to rule out.
2. Try a different port. Ports fail, and some ports on a machine provide less power than others.
3. Try a different computer. This distinguishes a drive problem from a computer problem, and it's worth doing before panicking.
4. Check whether it's a power problem. Larger desktop drives need mains power — check it's plugged in and switched on. Bus-powered drives draw power from the cable, and an unpowered USB hub often can't supply enough. Connect directly to the computer rather than through a hub.
A drive that spins up briefly and disconnects, or that clicks rhythmically on connection, is usually a power problem rather than a dead drive.
5. Check whether the system sees it at all. Open Disk Utility (Mac) or Disk Management (Windows). If the drive appears there but not in your file manager, it's a formatting or mounting problem, not a hardware one.
6. Check the format. A drive formatted for another operating system may not mount. A Mac-formatted drive won't appear on Windows without extra software. An NTFS drive appears on a Mac and is read-only.
7. Listen. Clicking, grinding, or beeping means a mechanical failure. Power it off and stop. Don't run repair tools; every additional minute reduces what can be recovered.
Formatting a new drive
New drives usually arrive formatted for Windows. If you're on a Mac, or want cross-platform use, reformat before putting anything on it.
Choose the format by job:
- Mac backup: APFS
- Windows backup: NTFS
- Shared between Mac and Windows: exFAT
- Connecting to a TV, console, or car: check the device manual, often exFAT or FAT32
Reformatting erases everything. If there's anything on the drive, copy it off and verify by opening files first.
Mac: Disk Utility → select the drive (the top-level device, not the volume) → Erase. Windows: Disk Management, or right-click the drive in File Explorer → Format.
While you're there, encrypt it. Both platforms support encrypted external drives. A backup drive is a complete copy of your life, and losing an unencrypted one is a serious exposure. Store the password in your password manager.
Ejecting properly, and why it matters
Always eject before unplugging. Use the eject button in your file manager, or right-click → Eject.
The reason: the system buffers writes. When you copy a file and the progress bar completes, some of that data may still be in memory waiting to be written. Ejecting flushes the buffer and confirms it's safe.
Pulling a drive mid-write causes corruption ranging from one bad file to an unreadable volume. This is more likely on exFAT, which lacks the journaling that helps other formats recover from interruptions.
If a drive won't eject — "the disk is in use" — something has a file open. Close applications, particularly anything that might be indexing or scanning it. Backup software, media applications, and search indexers are the usual culprits. If nothing obvious is holding it, logging out or restarting releases it.
Don't force-eject repeatedly. It defeats the purpose.
Using a drive with a phone or tablet
Modern phones and tablets support external drives, which is genuinely useful for offloading camera cards while travelling.
What you need: the right adapter for your device's port, and a drive the device can power. Bus-powered portable drives usually work; larger desktop drives usually don't unless separately powered.
Format: exFAT is the most widely compatible. Some devices are fussier than others.
How to use it: the drive appears as a location in the files application, alongside cloud services and local storage. You can copy files in both directions.
A powered USB hub solves the power problem if the device can't supply enough on its own.
The caveat: this is a convenience, not a backup. A drive you copy photos to while travelling is one copy on one device sharing a bag with the phone that took them. Useful as a second copy; not sufficient as the only one.
Using a drive with a TV, console, or media player
Devices with USB ports vary enormously in what they accept.
Check the manual for: supported formats (often FAT32 or exFAT), maximum capacity, whether it needs a specific folder structure, and whether it can power the drive.
Common problems: the drive is formatted in a way the device doesn't read, the drive is larger than the device supports, or the device can't supply enough power for a bus-powered drive.
Consoles often reformat drives for their own exclusive use, making them unreadable elsewhere. Read the warnings before agreeing.
Using one drive with several computers
Workable, with two considerations.
Format: exFAT, so both systems can read and write.
Ejection discipline: more important than usual, since exFAT is less resilient to interrupted writes.
Permissions: exFAT doesn't carry permissions, which is usually what you want for a shared drive.
Better alternative for regular use: share a folder over your local network instead. Both systems support this, it avoids the formatting compromise, and nobody has to carry anything.
Habits worth building
Label your drives physically. A sticker with what's on it and the purchase date. A drawer of unlabelled identical drives is a drawer nobody will ever sort out.
Keep a manifest. A text file on each drive listing what it holds and when it was last updated. When you plug it in after a year, this tells you immediately what you're looking at.
Verify after copying. Compare file counts and total size, and open several files including something large and something old. Copy operations fail partway more often than people expect, and quietly.
Plug archive drives in annually. Confirm they read, copy anything new, note the date. A drive untouched for five years may not read, and finding out early is the point.
Replace every three to five years, regardless of apparent health. Copying from a healthy drive is easy; copying from a failing one is not.
Never let a drive be the only copy of anything. An external drive is one device with a finite life.
The quick troubleshooting order
- Different cable
- Different port
- Different computer
- Check power — direct connection, not a hub
- Check Disk Utility or Disk Management
- Check the format
- Listen for mechanical noises — if present, stop immediately
Steps one and two solve the majority of cases. Step seven is the one where doing nothing is the correct action.
Next in this series: Router, Wi-Fi, and Network Basics for Home File Sharing