What is Purgeable Data on macOS and how to reduce it

9 min read

Your Mac is smart enough to understand what files are redundant and can be removed. Your Mac calls these files Purgeable Data. Usually, it’s about outdated caches, duplicates, and any kind of files that can be deleted without any impact on your system. 

To see purgeable data, you should enable the Optimize Storage feature on Mac. Go to the Apple menu, click About this Mac, and then the Storage tab. If you’ve activated storage optimization, you’ll see that next to color-coded sections for Documents, Apps, Photos, etc, there’s one called Purgeable. 

The Optimize Storage feature allows you to quickly identify files that are taking up lots of space on your startup disk and either delete them or move them to iCloud, depending on the type of file. There are a couple of different ways to use it, one of which uses CleanMyMac and which adds an extra tab – ’System Junk’ – to the Manage Storage window. Here’s method one.

What is purgeable memory?

Purgeable memory is slots of memory on your Mac that contain information, e.g. data or files, that can be removed by your operating system when more space is needed for running the system or saving new data.

Since your operating system can remove these files on its own in order to meet its memory space needs, you don’t have to worry about running out of space due to these items. If you’d like to clear purgeable space on your Mac yourself, read on.

The fastest way to clear Purgeable space from Mac

If you have CleanMyMac X installed on your Mac, you’ll have noticed an additional section  – System Junk. These are system files CleanMyMac has identified that can be safely trashed. All you need to do is click on System Junk and click Run.

cleanmymac smart clean

If you don’t have CleanMyMac installed, it’s available in Setapp – just launch Setapp, search for CleanMyMac and click Install.

Here’s what to do next.

  1. Launch CleanMyMac, click the Smart Scan tab, and then click Scan. 
  2. When CleanMyMac has finished scanning, click Run to perform the cleaning.

Also, you can perform cleanup with the Cleanup section – System Junk, Photo Junk, Mail attachments, etc, and review the results. You may be surprised by the results and by just how much space you can reclaim.

To see in detail what CleanMyMac has found in each section, click Review Details. From there, you can uncheck any items you don’t want to delete. When you’re ready, click Clean to delete the junk.

Clean up storage with CleanMyMac

When you’re done, you should have got rid of several gigabytes of purgeable data and freed up lots of room on your hard disk.

How to reduce Purgeable space manually

It’s always better if someone can do the cleaning for you, both at home and on your Mac. Nevertheless, it’s a good idea to learn how to free up space manually. While purgeable information can be restored at any time, there’s a little risk you’ll remove any important data:

  1. Click on the Apple menu at the left of the Finder menu bar and choose About this Mac.
  2. Click the storage tab and you’ll see a bar with different colored sections on it. Each of these sections describes a specific type of data. Documents is first, followed by System, then Apps, and so on. Towards the right, you’ll see a section called Purgeable. How to preview Purgeable storage in macOS
  3. Click Manage to free up space on your Mac. The next window that opens, launches with the first tab on the left, Recommended, selected. You’ll see four options. The first allows you to store all files on the Desktop or in your Documents folder in iCloud and only keep those you’ve opened recently on your Mac. To enable it, Click Store in iCloud. Manage your data
  4. The next three options allow you to remove movies and TV programmes you’ve already watched in iTunes from your Mac; empty the Trash automatically every 30 days; and review files in your Documents folder and delete any you don’t need.
  5. Once you’ve been through the Recommended options, you can click on the other sections on the left and follow the instructions to either delete files or review them before deciding what to do.

Delete purgeable space using Terminal

One solution users often share online to remove files in the purgeable space on their Macs is creating (and then deleting) a large file using Terminal. This forces the system to clear purgeable space in order to accommodate the large file, thus accomplishing the task of removing items in the purgeable space of your Macintosh HD.

Here’s the algorithm for creating a large file using Terminal commands — by creating a dummy file. Some users prefer to do this by creating an empty image disk in Disk Utility, but you can easily do the same in Terminal, and with more file type options to choose from.

Here’s the step-by-step. Open Terminal and move to the folder where you want to create your file using the cd command. For example, we moved to our Downloads folder to create the dummy file there.

  1. Type in ls and hit Enter. View the folders in your current directory and choose one of them where you want to create your dummy file. We chose Downloads.
  2. Type in cd Downloads and hit Enter (replace “Downloads” with the name of the folder you chose).
  3. Type in mkfile 30m one.mov and hit Enter. Your new file will be created in the folder  you navigated to in the steps above.

“30m” in the command in our third step stands for file size of 30 MB. Replace this number with a larger number to force your system to purge the purgeable space; e.g. if you have 40 GB of free space on your Mac’s disk plus 10 GB of purgeable space, you need to create a file larger than 40 GB in order for the system to be forced to purge. Note that while “30m” stands for 30 MB, “30g” would stand for 30 GB.

You can name your file anything you like, so you can use “one.mov” as in our example or any other file name with a different extension that’s compatible with macOS.

After you are done, remember to drag your newly created file to Trash and then empty Trash. This way, your Macintosh HD purgeable space opens up but you don’t clog your machine with more junk files instead.

Optimize your Mac’s storage

Now that we’ve figured out how to delete purgeable files on Mac, let’s look at optimizing your storage. macOS actually has an Optimize Storage tool that you can use.

Go to the Apple menu at the top left of your screen and click About This Mac. Go to Storage > Manage….

You’ll see a number of Recommendations based on your usage, including Optimize Storage that removes movies and TV shows you’ve already watched (you can redownload them at any time, if you need to). Recommendations also include suggestions to store items in iCloud to save space on your device and empty Trash automatically.

optimize storage mac

Other methods for identifying and removing purgeable data

Disk Drill, also available in Setapp, has a Clean Up section, which allows you to identify and delete files you don’t need.

Identify Purgeable space with Disk Drill app

  1. Install Disk Drill from Setapp if you haven’t done so already.
  2. Launch it and click ‘Clean Up’ in the toolbar.’ In the next window, click ‘Let’s get started.’ Click on the drive you want to clean up, then click Scan.
  3. Disk Drill will now scan your Mac identifying all the files on the drive you selected. When it’s done, it will list the folders on the disk in order of the amount of disk space they are occupying. By default, it doesn’t display any system or hidden files. To display those, click on the left menu and select ‘All files (including system and hidden ones).’
  4. Starting at the top, click on the drop-down arrow to display files inside the folder. If there are more folders inside, click on the drop-down arrows on those. You’ll soon tunnel down to the files that are taking up the most space on your drive – they’ll be labeled in red.
  5. To change the way Disk Drill displays files, use the other menus. For example, you can display files by the percentage of the total disk space they use, or only display files that take up more than the space you specify.
  6. To delete a file you no longer need, click the checkbox next to it and click ‘Remove file.’

Another way to free up disk space is to get rid of duplicate files. Gemini, another app available in Setapp, does exactly that.

Get rid of duplicates

  1. Install Gemini from Setapp and launch it.
  2. Read the information cards that appear and click Next when you’re done.
  3. When you see the window with a big ‘+’ in it, drag a folder onto it to identify duplicates. For example, open a Finder window and drag your user folder onto the ‘+’.
  4. Gemini will start scanning the folder for duplicate files. When it reaches your iTunes and Photos libraries, it will ask you to open those applications. You can either do so, or skip them and Gemini will leave those libraries alone.
  5. When it’s finished, click Clean Up to remove all the duplicates it’s found, or click Review Duplicates to select the ones you want to remove yourself.
  6. In the review window, click on the drop-down arrow next to folders of duplicates, make sure they really are duplicates, then check the box next to the one you want to delete and click Remove.

Without regular cleanups, purgeable data can pile up on your Mac, lightning-fast. In fact, the redundant file caches and duplicates can occupy up to 30% of your disk space. That’s a lot of storage you could use for valuable things. With cleaning utilities and a few minutes of your time, you can free it up and forget about the problem of limited storage.

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