How to Find and Delete Duplicate Files on External Hard Drive on Mac: 3 Ways

2020-03-05 05:40:21 / Posted by Rosa Reyes to Utility Follow @ Rosa

This article will show you how to delete duplicate files on external hard drive on Mac in minute. Do you have duplicate, triplicate and even more copies of the same files on your external hard drive? To get rid of duplicate files all at once and make efficient use of space on your external (and internal) storage media, you can use deduplication software. Well, how to efficiently remove duplicates from external hard drive on Mac with such software? Please just read on.

Find and delete duplicate files on external hard drive on Mac with 1 click

If you are asking the question of how to delete duplicate files on external hard drive on Mac, then let’s start with the best method. There is more than one way to do the deletion. The most efficient and reliable way is to use a duplicate file finder remover.

Such an app is designed for the purpose of looking for and eliminating duplicate files on a Mac or PC or a mobile device. The good news is it can also work on external hard drives, USB flash drives, memory cards and other external storage devices.

For Mac users, Cisdem Duplicate Finder can be the best choice.

  • Work with Mac’s internal storage, external storage and cloud drives
  • Find all types of duplicates such as photos, music files, videos and docs and ebooks, etc.
  • Find similar images
  • Support iTunes, Music, Photos and iPhoto
  • Multiple scan methods, filtering options and preview modes
  • 8 selection rules (including Auto-Select) and 3 deletion methods
  • Easy to use
  • Offer high speed and flexibility
  • Help free up space and better organize files

Free Download

pie chart overview of duplicate files

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

Step 1. Download and install the recommended duplicate file finder for Mac. Launch it. Click the add icon the add icon. Select the external hard drive connected to your Mac and click Open. Click Scan.

add a external hard drive to scan for duplicate files

Step 2. Once the scan is finished, you can find all the duplicate files under the All tab. You can also view them by category, such as Documents, Images, Music, etc.

There are three preview modes, allowing you to conveniently preview different type of files without leaving the app. You can zoom in or out for better view.

preview duplicate files

Step 3. This app will automatically select duplicate files for you to delete with one click. There are other selection rules provided, such as Select Newest and Select Oldest. You can also select or deselect manually. When it comes to dealing with similar images, there are more rules available.

selection rules

Step 4. Make sure the unwanted dupes are selected. Click the Delete button in the bottom right corner, which will bring up a message box. Click OK to permanently delete the duplicate files on your external hard drive all at once.

remove duplicate files from external hard disk permanently

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 is going on.

How to reduce scan time and improve efficiency

I have a huge amount of files on my external hard drive. Is there a way to make the scan even faster?

You can exclude folders or files to reduce scan time. The trick is to the app's file size filter and Ignore List feature to exclude files and folders from scan. This way, you can reduce the scan time or prevent specific items from being scanned (and deleted).

If your primary purpose is to delete large duplicate files on your external hard drive and free up storage space, then you can go to General > Select Minimum and Maximum file size and set a minimum size. By doing so, you can set the app to ignore small files and thus decrease the scan time.

To prevent folder or files from be scanned, go to the Ignore list tab. Click the add icon and add folder or file path. In addition, you can exclude specific file formats by adding extensions.

exclude folders or file extensions when looking for duplicate files on external hard drives


Cisdem Duplicate Finder for Mac uses MD5 value checksum algorithm and can do byte-by-byte comparison. This duplicate file finder remover can provide Mac users with the best solution to find duplicate files on external hard drives. It can scan quickly for any type of dupes.

Before clicking the Scan button, you can customize settings based on your need. Click the gear icon gear icon in the top right corner, which will bring up a new window.

Under the General tab, go to the Removal method section. If you deal with duplicates on your Mac's internal storage, all these three methods are available. However, when it comes to duplicate files on an external hard drive, Move to Trash (which is the default option) won't work. If you stick to the default one, the selected unwanted dupes will be deleted permanently. The option Move to Folder is still available.

customize settings

Also, under the Selection tab, there are a number of rules available for selecting dupes for removal.

Manually find and remove duplicate files on external hard drive with 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 find duplicate files on external hard drive or Mac’s internal hard drive with Terminal. Note that it only finds 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 three 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.

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5 Comments Leave a Reply

  • 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.

    3 years ago REPLY
  • 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?

    3 years ago REPLY
  • 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.

    3 years ago REPLY
  • 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.

    3 years ago REPLY
  • 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.

    4 years ago REPLY