How to Find and Delete Duplicate Files on Mac and External Hard Drives

2019-01-11 05:18:16 / Posted by Rosa Reyes to Utility Follow @ Rosa

How to delete duplicate files on external hard drive on Mac? What is the best duplicate finder for Mac to find and remove duplicates from internal and external storage? You will find answers here.

As time goes, you may download and store more and more files on your Mac. The older your Mac is, the more likely your hard drive is running out of space. To free up space on Mac, one solution is to get rid of unwanted files such as duplicate files. Another solution is to transfer part of your files to an external hard drive. However, when you transfer files back and forth between your Mac and external hard drive, duplicate files may end up on both. With both solutions, it can help if you know how to find and delete duplicate files effectively.

How to find delete duplicate files on external hard drive or the internal one on Mac with software

How to delete duplicate files such as photos that are stored on an external hard drive? I have over 15,000 duplicate photos on my iPhoto, 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 which could help me to find and remove these duplicate photos on Mac? Any help will be greatly appreciated. ― Asked by a Mac user

Why are there so many duplicate files on my Mac? Duplicate files are almost inevitable and can be due to file transfer, unnecessary backup, app (such as iTunes) bugs, etc. They can also occur when you import files to Mac from an external hard drive where duplicates already exist.

Whatever the cause is, it’s important to clean them up. By doing so, you can free up storage space, keep your files more organized and improve efficiency. The good news is you can use software to scan your Mac and external hard disk, find the duplicates scattered around, and remove them all at once. Duplicate cleaner software varies in performance, efficiency, ease of use and accuracy. For Mac users, Cisdem Duplicate Finder can be the best choice. It:

  • can find and delete duplicate files on internal hard disk and external storage devices such as HD, USB flash drives, SD cards, etc.
  • uses MD5 value checksum algorithm and can do byte-by-byte checking. As a result, users can get accurate and safe results.
  • can fast scan files and precisely identify duplicate photos, songs, videos, documents, archives and other types of files. True duplicates can be found regardless of file name and location.
  • allows users to quickly find and remove duplicates in iTunes and Photos.
  • offers 2 scanning methods, 3 preview modes, auto-select feature and 3 removal options, among other things, to make sure that users can get rid of duplicate files in an effective and safe manner.
  • provides free trial.

Free Download

Instructions: How to use it

You can follow the steps to delete duplicate files on external hard drive, Mac or other devices using Cisdem duplicate file finder. Here we will take external HD as an example.

Step 1Add hard drives or folders to scan

Connect your external hard drive to Mac. Drag the hard drive into this app. Click the Scan button. You can stop scanning anytime, and real-time scanning results will be provided.

add mac internal hard drives and folders and external hard drives

Step 2View duplicate files

Once the scan is finished, click the Show Results button to view a pie chart overview. Duplicates files will be classified and displayed by file type such as images and music. You can sort them by name, size, etc. and search among them with keywords.

pie chart overview of duplicate files on mac external hard drive

Step 3Preview duplicate files (optional but recommended)

Three preview modes are provided, allowing you to easily preview side by side. Previewing can be useful. For example, before deleting duplicate photos on external hard drive on Mac, you can preview and compare them in detail side by side.

find duplicate photos on external hard drive mac

Step 4Remove duplicate files

By default, Smart Select will automatically select duplicates for you to delete. There are also other selection options such as Select Newest. Click the Delete button to eliminate duplicate images, audios, etc. from your external hard drive.

Note: You can recover deleted files in Trash. However, please note that selected files on the external drive can only be erased permanently.

remove the duplicate files

Tips: Customize your duplicate files removal

When you use this app to find and eliminate duplicate files on Mac and external hard drives, these tips can be useful.

Set minimum and maximum file size for scanning

Before you click the Scan button in the first step, click the gray setting icon in the upper right corner of the app’s interface. Under the General tab, you can easily specify the file size range to be scanned.

find and delete duplicate files cisdem duplicate finder setting

Select the removal option of your choice

Under General, you can choose Move to Trash, Remove Permanently or Move to Folder.

Ignore certain folders, files, or extensions

Under the Ignore List tab, you can exclude folders, files or file extensions from scanning. This would be especially useful when you scan the whole hard drive and want to skip certain folder(s).

find duplicate files on external hard drives mac exclude

Exclude or include hidden files when scanning

Also under the Ignore List tab, you can enable or disable the Ignore System Hidden Files and Folders option.

How to delete duplicate files on external hard drive on Mac without software

How to find and delete duplicate files on Mac and external hard drive? There is more than one way. You can use software to identify and eliminate duplicates or do it by hand. It's not easy to manually find all the duplicate items on your internal and external hard drives on Mac. And it will take a lot of time and patience. Anyway, here’s how.

1. Go to Finder, choose a folder where you think duplicates may exist, say Documents, and use shortcut Command-F. A search bar will appear.

How to find duplicate files on external hard drive Mac by hand? Just choose your external hard drive in the Devices sidebar and then enter the said keyboard shortcut.

2. 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.

find and remove duplicate iles on external hard drive on mac by hand

3. Sort the listed files by name or other parameters, take a look at them, and find the duplicate files on Mac. You can move the unwanted ones to Trash.


There is another option when you choose to find Duplicate files on Mac without using software. Note that it only find duplicates. You need to delete the files manually. Terminal comes with every Mac. Below is how to use it.

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

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

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.

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

In conclusion

Above are the three methods on how to delete duplicate files on external hard drive on Mac. Duplicate files can be a big space eater on your internal and external hard drives. If your Mac does not have enough space, it may run slowly, and there may not even be enough free space for macOS update. By getting rid of useless duplicate files with the help of software like Cisdem Duplicate Finder which is picked as the best duplicate file finder for Mac in 2018, you can make more storage room on your Mac. Do you think this guide on how to find and delete 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.

    2 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?

    2 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.

    2 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.

    2 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.

    3 years ago REPLY