How To Reformat A Seagate External Hard Drive | Fix Errors

A Seagate external hard drive can refuse to copy files, show up as read-only, pop error prompts, or appear on one computer and vanish on another. Most of the time it’s not “mystery hardware.” It’s a format mismatch, a messy partition layout, or a file system that got corrupted after an unsafe unplug.

Reformatting resets the drive to a fresh state. It also erases all data on it. If you want any files from the drive, copy them off first. If the drive won’t mount, jump to the troubleshooting section before you erase anything.

Before You Start, Decide What The Drive Is For

Formatting is only hard when you don’t know the end goal. Answer these two questions and the rest becomes mechanical:

• Which computers will use it? Windows only, Mac only, or both.
• What kind of data will live there? Big video files, project folders with tons of small files, backups, or casual file transfers.

Quick Picks That Work For Most People

• Windows only: NTFS.
• Mac only: APFS (newer macOS) or Mac OS Extended (older Macs).
• Windows + Mac sharing: exFAT.
• Older gadgets: FAT32, with a 4 GB single-file limit.

What Quick Format Does

A quick format rebuilds the file table and marks the space as empty. A full format on Windows takes longer and checks the disk surface for bad sectors. If your drive has started throwing read/write errors, a full format can reveal trouble early. If the drive has behaved fine and you’re switching file systems, quick format is usually enough.

Back Up The Right Way Before You Wipe

If the drive is readable, copy your data to a second location. For large folder trees, copying thousands of tiny files can be slow and fragile. A simple trick: zip the folder first so you move one file, then unzip it on the destination.

If your Seagate drive is tied to backups, pause those jobs before you format. A backup app writing in the background can cause failed formats and confusing “disk in use” messages.

How To Reformat A Seagate External Hard Drive On Windows

Windows offers two paths. The This PC window is fine when the drive shows one normal volume. Disk Management is the better choice when the drive shows extra partitions, unallocated space, or the wrong capacity.

Option 1: Format From The This PC Window

1. Plug the drive into a direct USB port on the computer.
2. Open This PC, right-click the Seagate drive, then choose Format…
3. Set File system to NTFS (Windows-only) or exFAT (Windows + Mac).
4. Leave Allocation unit size on Default.
5. Type a Volume label you’ll recognize later.
6. Tick Quick Format unless you’re chasing repeated errors.
7. Click Start and confirm the wipe.

Option 2: Clean Partitions With Disk Management

Disk Management is where you go when the layout is messy. Microsoft’s documentation on Disk Management concepts and actions helps if you want the official definitions of volumes, partitions, and the “unallocated” state.

1. Right-click the Start button and open Disk Management.
2. Find the external disk by capacity. Double-check so you don’t touch your internal drive.
3. Right-click each partition you don’t need and choose Delete Volume until the space becomes Unallocated.
4. Right-click the unallocated space, choose New Simple Volume, and accept the full size.
5. Assign a drive letter.
6. Choose NTFS or exFAT, keep allocation size on Default, name it, then finish.

Reformat A Seagate External Hard Drive On Mac

On macOS, Disk Utility does the job. The main “gotcha” is the sidebar view: you must select the physical device to change the partition map. Selecting only the volume can leave old partitions behind.

Erase The Device In Disk Utility

1. Connect the Seagate drive.
2. Open Disk Utility (Applications → Utilities).
3. In the menu bar, choose View → Show All Devices.
4. Select the top-level Seagate device in the sidebar.
5. Click Erase.
6. Set a Name.
7. Pick a Format:
   • APFS for Mac-only use on modern macOS.
   • Mac OS Extended (Journaled) for older Macs.
   • exFAT for sharing with Windows.
8. Set Scheme to GUID Partition Map.
9. Click Erase and wait for completion.

Reformatting A Seagate External Hard Drive For Mac And PC Use

If the drive will move between Windows and macOS, exFAT is the usual choice. It handles large files and avoids FAT32’s 4 GB per-file cap. It’s a good fit for moving videos, installers, photos, and work folders between systems.

One practical tip: format the drive on the Mac if your goal is Mac + Windows sharing and you hit random mount failures. Seagate’s manual notes that some Windows allocation unit sizes can stop macOS from mounting an exFAT drive. Their Optional formatting and partitioning notes call out that mismatch and the cross-platform trade-offs.

File System Choices In Plain Language

This table sums up the formats you’ll see most often when you reformat a Seagate external drive.

Partition Map Choices That Prevent Odd Drive Behavior

Besides the file system, there’s the partition map. On a modern external drive, the safest default is GUID Partition Map (GPT). It’s widely accepted by current Windows and macOS systems and tends to avoid “wrong size” surprises after a reformat.

When You Might See MBR

MBR is older. You may still run into it when a drive was used with older PCs or older media boxes. If a device demands MBR, label the drive clearly so you don’t mix it with your day-to-day storage.

Post-Format Checks That Catch Problems Early

After the format finishes, run a quick reality check before you load the drive with real data.

• Copy a folder with mixed file types, then eject the drive and reconnect it.
• Open the files from the external disk, not from your internal storage.
• Rename one file and delete another, then confirm the changes stick after reconnecting.
• If you chose exFAT for sharing, test on both Windows and macOS.

Fixes When Formatting Fails

When a format won’t start or won’t finish, match the fix to what you see on screen.

Drive Doesn’t Appear In Finder Or Windows File List

• Swap the USB cable and try a different port.
• Skip USB hubs and plug into the computer directly.
• If it’s a spinning HDD, listen for spin-up. No sound plus no activity light can point to the enclosure or cable.
• On Windows, check Disk Management for a disk with no letter.
• On Mac, open Disk Utility and switch to Show All Devices.

Drive Shows As Unallocated Or Not Initialized

That usually points to a damaged partition map. On Windows, Disk Management can create a new volume after you clear old partitions. On Mac, erasing the physical device recreates the map and the volume in one pass.

Format Button Is Greyed Out

• On Windows, delete the volume first, then create a new one.
• On Mac, select the top-level device, not only the indented volume.
• If the drive is being used by a backup tool, pause that task, eject the drive, then reconnect.

Write Protection Messages

Some USB adapters and card readers have a lock switch. If you’re using an adapter, try a direct connection. If the same write-protected behavior follows the drive across multiple computers, the enclosure electronics or the drive itself may be failing.

Repeated I/O Errors Or Clicking Sounds

If you see I/O errors, repeated disconnects, or loud clicking, treat the disk as unreliable. Stop repeated format attempts and prioritize copying off anything you can still read. Extra writes can overwrite data you might get back and can stress a failing drive.

One-Page Checklist For The Whole Job

Use this table as your “do it once, do it right” checklist while you work.

What Reformatting Does To Old Data

After a quick format, the old data may still exist on disk until it gets overwritten. After a full format and repeated writes, getting data back gets harder. If you formatted the wrong drive and the data matters, stop using the drive right away and avoid copying anything onto it.

When You Should Retire The Drive

If the drive drops offline during transfers, fails formats across different computers, or keeps returning I/O errors, treat it as a hardware issue. At that point, the safest play is to move any remaining readable files off the drive and replace it.

Send us your feedbackTell us what you thought about this post

Name * Email *

Your comment *

Quick check — what is …? *

Send feedback