How do I clear purgeable storage on my Mac?


Another frequently asked question is ‘How do I clear purgeable storage on my Mac?’

What is purgeable storage on Mac?

Purgeable storage is a feature that can be used to free up disk space on the Mac OS. When you enable purgeable storage, your Mac OS will use RAM as temporary storage when needed and store files there if it runs out of disk space for normal operations.

How it works?

The best way to explain purgeable storage is by example: Let’s say your Mac OS needs to open or save a large file so it looks for available drive space. If the drive has less than 15% of free space left, macOS starts using purgeable memory automatically. If it runs out of temporary memory, a notification will prompt users to delete some unused applications first before continuing. Obviously, this mechanism frees up a lot of disk space on your hard drive and boosts performance since you’re not wasting resources by opening and saving files to your hard drive.

Purgeable storage is limited in size, however, so it’s important to understand when macOS will start using this feature to free up disk space.

If your Mac runs out of temporary memory during a process that requires a lot of it, such as watching a video or editing a large photo, the Apple logo will appear on the screen for a few minutes until there’s enough space on your Mac to continue. Users can check how much purgeable memory they have left at any time by going into About This Mac > More Info… > Storage and checking Memory Available.


How to check for it?

Users can always manually clear some temporary storage if they need even more disk space right away. To do so, go to About This Mac > More Info… > Storage and clicking on Clear Memory Cache.

What causes purgeable storage?

The macOS install process typically leaves several gigabytes of “temporary” files on your drive in various temporary directories. These usually get cleaned up automatically when the system is rebooted, but this doesn’t always happen due to several bugs in Apple’s software and/or hardware drivers. Reasons, why the purgeable storage space may not be re-claimed, include:

1. macOS needs to be booted from a bootable volume that doesn’t have any other data on it – e.g., if /tmp still has old files from a previous installation(s) then the install process won’t be able to remove them or add its own temporary files via “diskboot” (a command used in the early stages of each macOS boot).

2. The user hasn’t waited long enough for /tmp to clean itself up after rebooting following an installation of macOS or Mac OS X – always allow at least a couple of hours for this to happen.

You will need to proceed cautiously from here…

3. The user has installed the new version of macOS / Mac OS X and then manually copied files back over from another drive/volume e.g., using Migration Assistant (these files still take up space). Alternatively, the user may have had old backups stored on their computer and these were restored after updating to the new version of macOS/Mac OS X – even though they’re not actually needed anymore, such backups will still be taking up space until they’re deleted, which can prove difficult if they’re located in different places around the file system.

4. The purgeable storage is full again because a large file has been downloaded and quickly copied to the folder, rather than being moved or deleted. The system has no way of knowing that this file does not need to remain on the system and so it will take up storage space again until either the file is removed (either by moving/deleting it) OR until purgeable storage is completely used up and more space is needed.

5. Finally, if an external drive containing a Time Machine backup was unmounted without first disabling its Time Machine backup then there may be multiple backups taking up large amounts of space – each one cannot be automatically purged from the machine when they are not in use because macOS / Mac OS X needs to keep these backups in case they are ever needed to recover lost data.

How to clear purgeable storage on your Mac?

Purgeable storage refers to the data stored in “temporary” files and directories that macOS creates when it runs out of space for normal filesystem operations; if you’re not using enough storage, you’ll start running out of purgeable storage space.

Most iOS devices (including the iPhone) use Flash Memory for storing data; whereas Apple’s Macs generally use solid-state drive (SSD) technology for storing user files and applications/system files on the computer’s internal disk. SSD performs much better than HDD (magnetic disks); however, is more expensive to manufacture in large capacities.

Purgeable storage can be cleared by using commands in the terminal, this is an advanced method that should only be used if you are confident that you know what you are doing. If not, our mac repair experts are always ready to help!

  1. Open Terminal on your Mac.
  2. Type:

$ hdiutil create -size 25g empty.dmg

created: /Users/enekoalonso/empty.dmg

This should flush the purgeable storage.


I am a computer engineer holding a bachelor's degree in Computer Science, complemented by a Master's in Business Administration from University of Strathclyde, Scotland. I currently work as a Senior IT Consultant in Melbourne, Australia. With over 15 years of...