How To Clean the Scratch Disk on Mac

Scratch disk is a space on the hard drive that certain programs such as Adobe Photoshop and Final Cut Pro need in order to function properly. This dedicated virtual space is used by the apps as virtual memory whenever there is not enough physical memory available. The scratch disk can also be described as a space where temporary project files are stored while they are open in their respective program. 

If Photoshop, or other similar apps, are not exited properly, however, these temporary files might not get flushed or deleted. They could pile up and start earring the free space available on the scratch disk. As a result, users might encounter the 'scratch disks are full' error. Other causes of the same error might include lack of space on the entire drive that hosts the scratch disk, the specific partition used by the app being full, or limited RAM available to the app. As Photoshop is the most common culprit behind the ''scratch disks are full' error appearing on Mac systems, let's start with several solutions concerning this particular product. 

Clear the Photoshop cache

You can clear the Photoshop caches from inside the program itself. Just open an image in Photoshop and follow the steps:

  1. Go to the 'Edit' menu.
  2. Hover above the 'purge' option to reveal 4 different choices - Undo, Clipboard, Histories, All. Do note that if all four are greyed out, that means that the cache is currently empty. 
  3. Select one of the options or choose 'All' to clear all of them.
  4. You will be presented with a warning stating that purging the selected caches cannot be reversed so make sure that no important data will be lost before continuing. 
  5. Click 'OK.'

Manually delete temp files

Users can also attempt to manually delete the temp Photoshop files currently being stored on their Mac devices. First, let's locate the files. Usually, their names will begin with 'pst,' followed by a string of numbers, and finally '.tmp' as an extension. Try searching for Photoshop Temp on the selected drive or take the recommended route of searching the entire computer. Wait for the search to complete. Once the process is complete, you should be presented with a list of temp Photoshop files. Make sure that your projects are saved and the app is closed before proceeding to delete any, or all, of the files. 

Select a different scratch disk directory

If the current disk is rapidly losing the last free space it has, you could decide to simply move the scratch disk to a different hard drive that has more available space. A quick way to change the Scratch Disk location is to press the Command + option keys on your keyboard while launching Photoshop. Another method is:

  1. Select the Photoshop menu.
  2. Open 'Preferences.'
  3. Go to 'Scratch Disk.'
  4. Tick the checkbox used to select or remove a drive as the scratch disk location.
  5. Click 'OK.'
  6. Restart Photoshop. 

Flush the RAM via Terminal

If the ''scratch disks are full' error is caused by insufficient RAM, you can try to fix it by flushing the memory through Terminal:

  1. Open Terminal via Launchpad.
  2. Type the sudo purge command in the Terminal window.
  3. Enter your password if required. 

Dealing with the ''scratch disks are full' error on Windows computers

Users who want to clear the scratch disk on a Windows system can do so by following these steps:

  1. Open Photoshop.
  2. Go to 'Edit.'
  3. Open 'Preferences.'
  4. Select 'Scratch Disks.'
  5. Note the specific drive used as a scratch disk.
  6. Check the available free space on the specific drive. If it is below 40GB, you might need to access the drive and free up space by deleting or moving unused files and apps.

Windows users can also try to delete any temporary Photoshop files by themselves. Close all Adobe products and then go to the following location - C:\Users\Your Username\AppData\Local\Temp. Once there, look for files that contain 'Photoshop Temp' as part of their names and delete them.