Fix Scratch Disk Is Full Error on Mac

The “scratch disk is full” error on a Mac happens when Photoshop (or another Adobe app) runs out of the designated temporary storage space it needs to work smoothly. The fix is to free up space on your startup drive, add a new scratch disk, or change your scratch disk preferences to point to a drive with more room.

What Is a Scratch Disk?

A scratch disk is a designated area of your hard drive that Adobe apps like Photoshop, Premiere Pro, and After Effects use as a temporary workspace. When you’re editing a large image, applying filters, or working with a complex video timeline, the software needs a place to store intermediate calculations and history states. This data is too large to keep entirely in RAM, so the app writes it to a scratch disk. The scratch disk is not a separate physical disk; it’s simply a folder on your drive that the app uses for this purpose.

If the scratch disk becomes full, the app can’t write new temporary data, and it either slows to a crawl or stops working entirely, showing the “Scratch Disk Full” alert. This is different from your system’s regular memory (RAM), and it’s also separate from the file you’re actively saving. The scratch disk is a working space, not a storage space.

Why Does the Scratch Disk Fill Up So Fast?

Several factors contribute to a full scratch disk:

Large file sizes: Working with high-resolution images (e.g., 50-megapixel RAW files) or long 4K video projects generates enormous amounts of temporary data.
Many history states: Photoshop stores a record of your edits so you can undo them. Each history state takes up scratch disk space. The default number of history states is 50, but you can reduce it.
Multiple open documents: Each open document uses scratch disk space, even if you’re not actively editing it.
Low RAM: If your Mac doesn’t have enough RAM, the app has to use the scratch disk more heavily to compensate, filling it faster.
Small startup drive: If your main drive is nearly full, the scratch disk has very little room to grow. macOS itself also needs free space for virtual memory and other system tasks.

How to Fix the Scratch Disk Full Error

Here are the most effective fixes, in order of what to try first:

Free up space on your startup drive. The most common cause is simply that your Mac’s hard drive is almost full. Delete unused files, empty the Trash, clear caches, and move large media files to an external drive. You need at least 10-15% of your drive free for the system and apps to work comfortably.
Change the scratch disk location. In Photoshop, go to Photoshop > Settings > Scratch Disks… (on Windows, it’s Edit > Preferences > Scratch Disks). Uncheck your startup drive and check a different drive with more free space, like an external SSD. You must restart Photoshop for the change to take effect.
Add a new scratch disk. If you don’t have another internal drive, connect an external SSD. It should be fast (USB 3.0 or Thunderbolt) and have at least 50GB of free space. Then set it as the primary scratch disk in the same preferences menu.
Clear the current scratch disk. The scratch disk files are stored in a hidden folder. To clear them, quit Photoshop, then restart your Mac. This clears the temporary files. You can also go to Go > Go to Folder… in Finder and type ~/Library/Application Support/Adobe/Adobe Photoshop [version]/ and delete the contents of the Adobe Photoshop [version] Settings folder, but be careful—this will reset your preferences.
Reduce history states. Go to Photoshop > Settings > Performance and lower the “History States” number (e.g., from 50 to 20). This reduces the amount of data stored on the scratch disk.
Close other apps. If you have many apps open, they’re using RAM and disk space. Close everything you’re not using, especially other Adobe apps like Lightroom or Illustrator.

Preventing the Error in the Future

Once you’ve fixed the immediate problem, take these steps to avoid it happening again:

Keep your drive clean: Regularly delete files you don’t need. Use a tool like CleanMyMac or just manually empty your Downloads folder and Trash.
Use an external scratch disk: If you regularly work with large files, invest in a fast external SSD and dedicate it as your scratch disk. This keeps your startup drive from filling up.
Increase RAM: If your Mac allows it, adding more RAM will reduce the reliance on the scratch disk. This is the most effective long-term solution for heavy users.
Monitor your free space: Keep an eye on your drive’s free space in Finder. If it drops below 20%, take action before you hit the error.

What If the Error Persists?

If you’ve tried everything above and the error still appears, there are a few more advanced steps:

Repair disk permissions: Open Disk Utility (in Applications > Utilities), select your startup drive, and click First Aid. This can fix minor file system issues that might be causing problems.
Reset Photoshop preferences: Hold down Option + Command + Shift while launching Photoshop. This will reset all preferences to default, which can clear corrupted settings that are causing the scratch disk to fill up.
Reinstall the app: As a last resort, uninstall and reinstall Photoshop. This ensures a clean installation without any corrupted files.

Common Misconceptions

One common misconception is that the scratch disk is a physical component you can replace. It’s not—it’s just a folder. Another is that clearing the scratch disk will delete your work. It won’t; it only removes temporary files. Also, some users think that increasing the scratch disk size in preferences is a solution, but there’s no such setting—the scratch disk uses all available free space on the designated drive. Finally, the error is not exclusive to Photoshop; other Adobe apps like Premiere Pro and After Effects have the same issue and can be fixed with the same methods.

Frequently Asked Questions

How much free space should I have on my Mac to avoid this error?

It’s recommended to have at least 15-20% of your startup drive free. For a 256GB drive, that’s about 40-50GB. This gives macOS and your apps enough room for temporary files and virtual memory.

Can I use a USB flash drive as a scratch disk?

Technically yes, but it’s not recommended. USB flash drives are slow and may not be reliable for the constant read/write operations. An external SSD is a much better choice.

Will the scratch disk error affect my saved files?

No, your saved files are safe. The scratch disk is only for temporary data. However, if the error occurs while you’re working, you might lose unsaved changes if the app crashes.

How do I check which drive is being used as the scratch disk?

In Photoshop, go to Photoshop > Settings > Scratch Disks. The drives that are checked are the ones being used, in order of priority.

Why does the error appear even when I have plenty of free space?

This can happen if the scratch disk is set to a drive that’s actually full, or if the app is using a drive that has permissions issues. Check your scratch disk settings and ensure the selected drive has free space and is writable.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

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