The "scratch disks are full" error stops Photoshop cold, usually right when you are mid-edit and least expecting it. It means the drive Photoshop uses for temporary working files has run out of room. The good news is that clearing it is quick, and you rarely need to reinstall anything. By default, Photoshop uses your Mac's boot drive as its scratch disk, and Adobe suggests keeping at least 20 GB of free space there for scratch work. Below are eight fixes we have run through real cleanup sessions, from purging the cache to moving the scratch disk to an external drive.
How to Clear Your Scratch Disk on Mac (8 Fixes)
Work through these in order. The early fixes are the fastest and solve most cases, and the later ones prevent the error from coming back.
1. Clear the Photoshop cache
Photoshop stores undo states, clipboard data, and history in a working cache that grows fast during a long session. Clearing it frees scratch space immediately without touching your file. Open the app, go to Edit > Purge, then choose All or a single category such as Histories or Clipboard.
One caution from our own sessions: Edit > Purge cannot be undone. Once you run it, any earlier undo or history state is gone, so save your work first. If you only need to reclaim a little space, purge Histories on its own and leave the rest intact.
Purging is irreversible. Save the document before you run Edit > Purge, because every undo step and history state disappears the moment you confirm.
2. Delete Photoshop temporary files
Here is the detail most guides skip: Photoshop only deletes its own temp files when it closes cleanly. A crash, a power loss, or a force-quit leaves orphaned files behind, and they pile up until the disk reports full. In our cleanups, force-quitting Photoshop instead of closing it normally was the single most common reason a scratch disk suddenly filled.
To clear the leftovers, quit Photoshop first. Then open Finder, press Shift + Command + G, and go to /tmp. Look for files that start with a Photoshop prefix such as pst and end in .tmp. Those are safe to delete once the app is closed. Empty the Trash afterward to actually reclaim the space.
3. Free up disk and storage space on your Mac
Because the scratch disk defaults to your boot drive, a nearly full Mac and a full scratch disk are often the same problem. Open the Apple menu > About This Mac > Storage (Storage Settings on newer macOS) to see what is eating your space. Clear out large downloads, old installers, and the caches you no longer need.
Keep at least 20 GB free on the startup drive as a baseline, and more if you work with large, layered files. This is the fix that resolves the widest range of scratch-disk errors, so do not skip it even if the others tempt you.
For a manual walk-through, our guide on how to free up disk space on your Mac covers the same cleanup by hand. Apple also documents its built-in tools to free up storage on your Mac.
4. Change or move Photoshop's scratch disk to another drive
If your boot drive stays tight on space, point Photoshop at a different disk instead. Go to Photoshop > Settings > Scratch Disks (Preferences on older versions). You will see a checklist of available drives. Check a second drive with free room, and, if you have one, set it above the system drive in priority.
The one rule that matters: do not leave the system drive as the only scratch option. Adobe explains how to assign a scratch disk in Photoshop's preferences, and the change takes effect the next time you restart the app.
5. Move the scratch disk to an external drive
An external drive is a good permanent home for scratch work, and it keeps your boot drive clear. From experience, an external SSD, ideally an NVMe one, makes a far better scratch disk than a mechanical platter drive, both for speed and for reliability. Photoshop leans on the scratch disk constantly, so a slow drive drags the whole app down.
Assign it the same way as fix 4, through Scratch Disks in settings. One catch to plan around: the external drive has to stay connected whenever Photoshop runs. Unplug it, and you are back to the boot drive.
6. Increase Photoshop's RAM allowance
More memory means Photoshop offloads less work to the scratch disk in the first place. Open Photoshop > Settings > Performance and drag the Memory Usage slider higher. A setting in the 70 to 80 percent range works well on most Macs, while still leaving headroom for macOS.
This will not clear a disk that is already full, but it eases the pressure that fills it. Adobe's advice to optimize Photoshop performance covers the memory and scratch settings together.
7. Free up RAM using Terminal or Activity Monitor
When Photoshop feels sluggish and the scratch disk keeps filling, freeing memory helps. The reliable route is Activity Monitor, found in Applications > Utilities. Open the Memory tab, sort by memory used, and quit the heavy apps you are not using. Closing a memory-hungry browser alone often frees a surprising amount.
Some guides point to Terminal commands for this, but we do not recommend running memory commands you cannot verify. Activity Monitor does the same job safely and shows you exactly what you are closing.
8. Disable auto-recovery saving
Photoshop's auto-recovery and AutoSave features write extra data in the background, which adds to scratch and temp buildup during long sessions. If you save often on your own, you can lengthen the interval or turn the feature off. Go to Photoshop > Settings > File Handling and adjust the auto-recovery options there.
This is a smaller fix, best treated as fine-tuning after the bigger cleanups. Only disable auto-recovery if you trust your own save habits, because it is a genuine safety net during crashes.
What Is a Photoshop Scratch Disk (and Why It Fills Up)?
A scratch disk is the drive Photoshop uses as temporary working memory when your Mac's RAM runs out. Think of it as overflow space for the pixels, layers, and history states you are actively editing. Photoshop cannot function without one.
What "scratch disks are full" means
The message means the assigned scratch drive has no room left for Photoshop to keep working. What trips people up is that the error can appear even when the drive looks like it has free space. That usually happens because the boot drive is nearly full, or the scratch volume is fragmented or simply too small for the job. Photoshop needs contiguous working room, not just a few scattered gigabytes.
What causes the "scratch disks are full" error
The most frequent trigger we see is a Photoshop session that ended badly. Because the app clears its temp files only on a clean exit, every crash or force-quit leaves orphaned files behind. Over weeks, those add up and quietly claim the space Photoshop expects to have free.
A single forgotten file can eat the disk too. In one cleanup, an unused 100 GB file was taking over 20 percent of the system drive on its own. Large, layered projects, dozens of open documents, and a low memory allowance all push more work onto the scratch disk as well. Often it is a combination, not a single cause, so a quick audit of your drive pays off.
Photoshop only clears its temp files when it closes cleanly, so every crash or force-quit leaves working files stranded on your scratch disk.
How Do You Open Photoshop When the Scratch Disk Is Full?
This is the frustrating part of the error: sometimes Photoshop will not even launch, so you cannot reach the menus to fix it. There is a built-in shortcut for exactly this situation.
The Command + Option + Shift launch shortcut
Hold Command + Option + Shift while Photoshop is launching. Keep the keys pressed as the app starts, and the Scratch Disk Preferences dialog opens before Photoshop fully loads. From there you can point it at a drive with free space, then let it finish opening.
Time it right by holding the keys the instant you click the icon, and do not let go until the dialog appears. It is the single fastest way back into a Photoshop that refuses to start.
Locked out by a full scratch disk? Hold Command + Option + Shift while Photoshop launches. The Scratch Disk Preferences dialog opens first, so you can pick a drive with free space before the app loads.
How to Clear the Scratch Disk Without Opening Photoshop
You do not always need Photoshop open to free up its scratch space, which helps when the app will not cooperate. With Photoshop fully quit, most of the cleanup happens in Finder and macOS.
Start with the /tmp folder and delete the orphaned .tmp files described in fix 2. Then clear space on the boot drive through About This Mac > Storage, and empty the Trash. A dedicated Mac cleaner can automate the same steps if you would rather not hunt through folders. Once the drive has room again, Photoshop should launch normally, and you can reassign the scratch disk if needed.
How Much Scratch Disk Space Do You Need?
Adobe's baseline is a minimum of 20 GB of free space on the startup disk for scratch use. That figure is the floor, not a target. For everyday editing it is usually enough, but larger projects want far more headroom.
Complex, multi-layer files can call for considerably more, sometimes well over 100 GB during heavy work. Treat anything above the 20 GB minimum as headroom for big jobs rather than a hard requirement. If you regularly hit the limit, moving the scratch disk to a roomy external SSD is the durable fix.
The 20 GB figure is the minimum Adobe recommends, not the ceiling. Large, layered projects can need much more temporary space, so give yourself room to grow.
Long-Term Prevention Tips
A few habits keep the error from returning. Quit Photoshop normally instead of force-quitting, so it can clear its own temp files on exit. That one change prevents most repeat cases, since orphaned temp files are the usual culprit behind a disk that fills again and again.
Keep 20 GB or more free on your boot drive at all times, and clear the cache during marathon editing sessions. If you work with big files often, set a fast external SSD as your scratch disk and leave it connected. Skip the old habit of defragging, since modern Macs do not gain anything from it. Regular backups matter more than any tuning trick, because they protect the work itself if a drive ever fails.
We ran these fixes through real before-and-after cleanups on Mac, tracking what actually reclaimed scratch space. The steps here are ordered the way we would work through them ourselves, fastest and highest-impact first.
Frequently Asked Questions
What is a Photoshop scratch disk?
Why does Photoshop say the scratch disk is full when I still have free space?
How do I clear the scratch disk without opening Photoshop?
How do I open Photoshop when the scratch disk is full?
How much scratch disk space does Photoshop need?
How do I clear the scratch disk on Windows?
Does defragmenting help on a Mac?
If Adobe's own troubleshooting helps, its guide to troubleshoot the scratch disk full error walks through the same territory from the vendor's side.
Conclusion: Keep Your Scratch Disk Clear
Clearing a full scratch disk on Mac comes down to freeing room and giving Photoshop somewhere better to work. Start by purging the cache and deleting orphaned temp files, then free up boot-drive space and keep at least 20 GB clear. If the problem keeps returning, move the scratch disk to a fast external SSD and quit Photoshop cleanly every time.
Note the Command + Option + Shift launch shortcut for the days Photoshop will not even open. With these eight fixes in hand, a full scratch disk becomes a five-minute fix rather than a lost afternoon.
