How to Delete Duplicate Files on External Hard Drive on Mac

Rosa Reyes
time April 16, 2020 Preview 31.5K
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This article will show you how to find and delete duplicate files on external hard drive on Mac 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 computer to computer. 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 two ways for Mac users to remove duplicate files from external hard drive.

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

How to find duplicate files on external hard drive on Mac? The best way is to use duplicate file finder software like Cisdem Duplicate Finder for Mac. It is compatible with macOS 10.10 or later, including macOS 10.15 Catalina.

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

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

Download and install Cisdem Duplicate Finder. Open it.

Free Download

Click the add icon the add folder icon and add hard drives or folders to scan. Click the Scan button.

add drives to scan

  • To find duplicate files on an external hard drive, add the drive alone. Also, you can add specific folders from the drive.
  • To find duplicate files between two drives (internal or external), add these drives.
  • Likewise, you can use the app to easily scan for duplicate files across multiple drives or folders, external or internal.

Step 2. View and preview duplicate files

Once it finishes scanning, you will be presented with the results window. All the duplicate files are listed under the All tab. You can also view them by file type, such as Images, Music and Documents.

There are three preview modes (Thumbnail, List and Info), allowing you to preview pictures, media files and documents without leaving the app. The preview feature can be especially useful when it comes to deleting duplicate photos on external hard drive. You can also zoom in or out for better view.

view and preview duplicate files

Step 3. Select duplicates for removal

This duplicate file finder will automatically select duplicate copies for you to delete. Additionally, it provides four selection rules selection rules icon.

  • Smart Select
  • Select by Priority
  • Select Newest
  • Select Oldest

You can choose one of them based on your preference. Also, it allows you to select or deselect manually.

On a side note, when it comes to handling similar images, there are eight selection rules available.

selection rules

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

Make sure that you have selected the unwanted duplicates. Click the Delete button in the bottom right corner. A message will appear. Click Yes to confirm the deletion.

delete duplicate files on external hard drive on mac

The duplicates will be permanently removed from your external HD. If it were an internal disk instead of an external one, there would be more removal options available such as Move to Trash.

Note: You can stop the scan process at any time, and real-time scan result will be provided. Don’t eject your external hard drive while the scan or removal is going on.

Cisdem Duplicate Finder main features:

  • Detect and delete duplicates on Mac, external SSD/HDD, USB flash drives, SD card, Google Drive and more
  • Find duplicate photos, videos, audios, Word documents, spreadsheets, PDFs, ebooks, packages, archives, etc.
  • Also find similar images
  • Remove dupes from Photos, iPhoto, iTunes & Music
  • Scan for one or multiple folders or drives simultaneously
  • Allow you to scan for duplicates by file content or filename
  • Automatically select files for you to eliminate with 1 click
  • Also provide multiple selection rules
  • Easy to use
  • Free up space on Mac, external hard drive, etc.
  • Help you better organize your files

Free Download

Tip: How to reduce time to scan external hard drive for duplicate files

This Cisdem external hard drive duplicate file finder uses MD5 value checksum algorithm and does byte-by-byte comparison when scanning. It generally only takes seconds to scan thousands of files. For a significantly large amount of files, it will take more time.

Here’s the good news! You can exclude files and folders from the scan so as to lessen the time it will take.

  • Exclude folders Before you hit the Scan button, click the settings icon in the top right corner. Go to the Ignore List tab. Click the add icon to add specific folders or sub-folders for exclusion.exclude folders
  • Exclude file types Go to the Ignore files of particular extensions section. Click the add icon to enter file extensions. If you enter MP3, it will skip all the MP3 audio files when scanning your external HD for duplicates.
  • Exclude files by size Switch to the General tab. There, 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.exclude files by size

In addition to what has been mentioned in the tip above, there are also other options in settings settings icon. By customize settings options when needed, you will be rewarded with a more efficient duplicate removal.

Free Download

Manually find and delete duplicate files on your external hard drive in Finder

How to delete duplicate files on external hard drive mac such as photos that are stored on them? I have over 15,000 duplicate photos on my Photos, half of it stored on the external HD. I tried to find these duplicates manually, but it was a waste of time and energy. Is there a duplicate file finder what could help me to find and remove these duplicate photos on Mac? Any help will be greatly appreciated. ― Asked by a Mac user

How do Mac users find and delete duplicate files on external hard drive? The best way is to use a duplicate file finder for Mac. You can also do it by hand. It's not as hard as it seems. However, it can be a waste of time and energy if there are a lot of duplicate files on your external hard drive. Anyway, here’s how.

Step 1. Plug your external hard drive into Mac. Go to Finder. In the Devices sidebar, select the external drive.

Step 2. Use shortcut Command-F. A search bar will appear.

Step 3. Select Kind among the available search parameters. Select the file kind of your choice in the second dropdown list. Also choose a specific file format if needed.

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

Step 4. Sort the listed files by name or other parameters, preview and compare, and find the duplicate files. You can move the unwanted ones to Trash.

Use Terminal

You can also identify duplicate files on external hard drive or Mac’s internal hard drive with Terminal. Note that it only identify duplicates. You still need to delete the files manually. Terminal comes with every Mac.

Step 1. Go to Finder > Applications > Utility. Find and open Terminal.

Step 2. If you want to find the duplicate files in a folder, say Downloads, you can use the cd command by typing cd ~/Downloads and press the return key.

Step 3. Enter the command: find . -size 20 \! -type d -exec cksum {} \; | sort | tee /tmp/f.tmp | cut -f 1,2 -d ' ' | uniq -d | grep -hif – /tmp/f.tmp > duplicates.txt. Press return.

Step 4. Open the file duplicates.txt and you will find a list of duplicate files. Now you can manually find and delete them.

Why there are so many duplicate files and how to avoid them

Why are there so many duplicate files on my Mac? It’s not uncommon to have duplicate files on your Mac and external hard drives. As a matter of fact, duplicate files are almost inevitable.

They can be there due to multiple imports of the same file, multiple copies of backup, app (such as iTunes) bugs, etc. They can occur when you unknowingly transfer files to your external hard disk where the same files already exist. Another cause is file compression. Sometimes we compress photos to make them smaller in size for emailing or uploading. In a case like this, there can be duplicate copies of the same photos. They are identical in content but different in size.

Whatever the cause is, it’s important to clean them up. By doing so, you can free up storage space and keep your files more organized. It will also help if you know how to prevent them from occurring.

  • Delete photos and videos from SD card after you transfer them to your Mac
  • Set your Mac to detect duplicate files while importing
  • Be aware that resizing or editing photos will lead to almost duplicate files
  • Avoid unnecessary backups
  • Use duplicate file finder software on a regular basis

In conclusion

Above are the two common ways on how to find duplicate files on external hard drive on Mac. Duplicate files can waste space your internal and external hard drives. By getting rid of useless duplicate files with the help of software like Cisdem Duplicate Finder, you can free up storage space on your external hard disk. Do you think this guide on how to identify and remove duplicate files helpful? Leave a comment and share your thoughts and opinions.

Rosa Reyes
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Rosa has worked in Mac software industry for more than eight years. She believes that the purpose of software is to make life better and work more productively. In addition to writing, Rosa is also an avid runner.

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Comments (4) Leave a Reply

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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.

    5 years ago Reply

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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?

    5 years ago Reply

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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.

      5 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.

    5 years ago Reply

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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.

    5 years ago Reply

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