How to Delete Duplicate Files on External Hard Drive on Mac and PC

Sarah Miller
Updated on July 01, 2024 Preview 44.2K Preview 6
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This article shows you how to find and delete duplicate files on external hard drive on Mac and Windows PC easily and quickly.

External hard drives are often used for backup purposes such as Time Machine backups. They can also be used to transfer files from one computer to another. Duplicate files may slowly accumulate over time as you use your external hard drive. To make effective use of the storage space on your drive, it’s a good idea to find the duplicate files on it and get them deleted. The article talks about easy ways to remove duplicate files from external hard drive.


(Note: Cisdem Duplicate Finder also has an Android version, which can find and delete duplicate files on Android devices for free.)

Part 1. Find and delete duplicate files on external hard drive on Mac and PC in 1 minute or less

To find duplicate files on an external hard drive, the best way is to use Cisdem Duplicate Finder, a duplicate file finder app. This app can accurately and quickly identify duplicate files (exactly identical files regardless of name) on your computer’s internal hard drive, external storage devices, and even cloud storage services and allows you to easily and quickly to remove unwanted duplicates.

In addition to duplicate images, the app can find non-exact duplicates (photos that look the same but are different in resolutions, file sizes or formats) and similar photos.

Delete duplicate files on external hard drive on Mac or Windows in 4 steps

Step 1. Add your hard drive(s) to scan

Download and install Cisdem Duplicate Finder. Open it.

Free Download macOS 10.11 or later Free Download Windows 11/10/8/7

Click the Add button the add folder icon to add your external hard drive. Click the Scan button, and this app will start finding duplicate files on this external hard drive.

add drives to scan

  • To find duplicate files on a drive (or in a folder on it), external or internal, add this drive (or folder) alone.
  • To find duplicate files between two drives, external or internal, add both drives.
  • To find duplicate files across multiple drives, external or internal, add these drives.

Step 2. View and preview duplicate files

When the app finishes finding, the results window will appear, displaying all the duplicate files found on your external hard drive under the All tab. You can also view different types of duplicate files (such as duplicate photos) under the corresponding tabs (such as the Image tab).

There are three view modes (Thumbnail, List and Info), allowing you to easily preview images, audios, videos and documents and view file information like name, size, location and resolutions. The preview feature can be especially useful when it comes to deleting duplicate photos on external hard drive. You can zoom in or out the preview for a better view.

The Similar Image tab displays non-exact duplicate photos and similar photos.

view and preview duplicate files

view similar images

Step 3. Select duplicates for removal

In each set of duplicate files, this duplicate file finder has automatically selected all but one file for deletion. You can also select/deselect by hand. In addition, there are selection rules selection rules icon to help you mass select.

a list of the eight selection rules

Step 4. Delete duplicate file on external hard drive with 1 click

Once you are sure that all unwanted duplicates are selected. Click the Delete button in the bottom right corner. Click OK in the message that appears to confirm the deletion.

delete duplicate files on external hard drive on mac

The duplicates will be permanently removed from your external hard drive. If it were your computer’s internal hard drive instead of an external one, more removal options (such as Move to Trash/Recycle Bin) would be available.

Important: Please don’t eject your external hard drive that is connected to your computer while the scan or removal of duplicate files is going on.

Tip 1. How to reduce the time to scan an external hard drive for duplicate files

It generally only takes seconds to compare thousands of files to identify duplicates. If there are a significantly large amount of files, the scan will take more time. Luckily, you are allowed to reduce the scan time by excluding files and folders from the scan.

Before you click the Scan button in step 1, click the settings icon the settings icon in the top right corner. In the settings window that appears, you can exclude items.

  • Exclude folders In the Ignore folders and files in the list section, add the folder(s) of your choice for exclusion. For example, you can exclude a folder that you are sure doesn’t contain duplicate files.
  • Exclude file types In the Ignore files of particular extensions section, enter file extensions of your choice. For example, if you enter MP3, it will skip all the MP3 files when scanning your external HD for duplicates.
  • Exclude files by size You can set the minimum and maximum file size. For example, if you aim to get rid of large duplicate files and quickly free up space on your external hard disk, then you can set the scan to skip all small- and medium-sized files.

the settings window showing settings to exclude items from scan

Tip 2. Customize how the identification of duplicate photos works

Strictly, there are two types of duplicate photos: the ones that are exactly the same regardless of name, and the ones that look identical but are actually slightly different. To find both types of duplicate photos on your external hard drive, please go to the settings window to turn on similar image detection. This tip may be particularly helpful for photographers, amateur or professional.

the settings window showing that similar image detection is turned on


Part 2. Manually find and delete duplicate files on your external hard drive

How do you find and delete duplicate files on an external hard drive? The recommended way is to use a duplicate file finder due to the great ease and efficiency. But if there aren’t many files on your external hard drive, you can try getting rid of duplicate files on it manually by using the built-in file manager on your computer.

Use Finder

Applies to: Mac computers

Finder is a file manager included in macOS. Below is how to use it to get the job done.

Step 1. Connect your external hard drive to your Mac using a cable. Open Finder. In the left sidebar of Finder, select this drive.

Step 2. Press Command-F to bring up the advanced search in Finder.

Step 3. In the pop-up menu on the left, choose Kind. Choose a file kind/type in the next pop-up menu. (You can further choose a specific file format if needed.) Now the Finder window displays all the files of your chosen kind on your external hard drive.

manually find duplicate files on external hard drive with Finder on Mac

Step 4. Choose the sort order that makes it easy for you to compare files to identify duplicate files, such as Name or Size. The Preview pane on the right of Finder can greatly help you compare files.

Step 5. In each set of duplicate files that you’ve found, move the unwanted one(s) to Trash.

Step 6. Repeat steps 3 to 5 to remove another type of duplicate files.

You can also identify duplicate files on external hard drive on your Mac with Terminal, an app included in macOS. But note that this method is not that user-friendly. Also, this method only identifies duplicates. You still need to delete duplicates manually. Here’re the details of this method.

Use File Explorer

Applies to: Windows computers

File Explorer is a file manager included in the Windows operating system. Below is how to delete duplicate photos on external hard drive with File Explorer, which can also help you deal with other types of duplicate files.

Step 1. Connect your external drive to your PC.

Step 2. Press Win + E to open File Explorer. Navigate to your external hard drive.

Step 3. Click on View > Details.

Step 4. Click on Sort > Group by > Size.

sort files

Step 5. In the search box in the top right corner, type in “kind:=picture”.

Step 6. Go through the photos displayed in the File Explorer window to find duplicates by comparing photos.

Step 7. Delete the duplicate files you have found.



Why are there duplicate files on your external hard drive?

There could be various reasons. Here’re some possible ones.

  • When you backed up files using your external hard drive, duplicate files already existed in the files you backed up.
  • Or, you, most likely unintentionally, used it to back up the same files twice or more.
  • When you organized files on your drive, you moved files by copying and pasting instead of using drag and drop.

Knowing the reasons may help prevent duplicates from occurring in the first place.

How do you avoid duplicate files on an external hard drive?

These are 5 suggestions may help you prevent duplicate files on external hard drive:

  • Avoid unnecessary backups.
  • Delete files on your external hard drive after you transfer them to your Mac or PC, if you think that it’s unnecessary to keep them there anymore.
  • Use duplicate file finder software on a regular basis.
  • Name your files in a logical way, which may help you quickly and easily identify duplicates.
  • Use drag and drop instead of copy and paste when you move files to a folder.



Duplicate files can waste space on computers and external storage devices. Getting rid of useless duplicate files on your external hard drive can free up storage space and make room for new files or backups. This article talks about two ways on how to identify and delete duplicate files on external hard drive on Mac or Windows PC. I hope it’s helpful.

Sarah Miller
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With a passion for tech and writing, Sarah joined Cisdem, where she focuses on creating articles about using utility tools to enhance file management and simplify contact management.

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Comments (6) Leave a Reply

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  • Kerstin Olesch

    Thank you so much. The duplicate file finder tool you recommended is easy and quick to use. Saved me a ton of time and space on my hard drive!

    1 years ago commonReply

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  • Limnos

    I have a lot duplicate picture and movie files on my MacBook, this duplicate file finder app helped me free up 53GB space. I can't express my gratitude in words.

    7 years ago commonReply

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  • Melissa

    I want to delete duplicate files from other storage device, not only from Mac or external hard drives, can Cisdem duplicate file finder help me do that?

    8 years ago commonReply

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    • Rosa Reyes

      Hi, Melissa, Cisdem DuplicateFinder fully supports deleting duplicate files from Mac HDD, SSD, external hard drives, cameras, iPods, USB flash drives, memory cards, etc.

      8 years ago
  • Lareina

    My hard drive seems to create "duplicates" of all my files. I don't want to check it one by one. Cisdem DuplicateFinder did a great job with works very well and remove duplicate files from my external hard drive quickly.

    8 years ago commonReply

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  • Phoebe

    My mac was running out of space, and i transferred many files to external hard drive. I found many duplicate photos and music and tried to delete them manually. Oh, my god, I even didn't know there is such a nice tool like Cisdem DuplicateFinder that can help me remove them.

    8 years ago commonReply

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