Photoshop "Scratch Disks Are Full" Error: 7 Fixes That Actually Free Space

The "scratch disks are full" error stops Photoshop cold, usually mid-project, and the fix is rarely obvious. Photoshop uses a scratch disk as overflow RAM, and when that volume runs out of writable space, the app refuses to proceed. This guide walks through seven concrete fixes in order of speed and impact, covering cache purges, orphaned temp files, scratch disk reassignment, and getting your overall SSD back under a healthy threshold.

What Is the Scratch Disk and Why Does It Fill Up?

When Photoshop runs out of RAM to hold your history states, open documents, and compositing buffers, it spills data onto a designated scratch disk volume. By default, that volume is your startup disk. On modern Macs with limited SSD free space, even a single large PSD with many history states can push it over the edge.

The could not complete request scratch disk error (and its variant "scratch disk full error photoshop") appears as soon as Photoshop cannot write more scratch data. The volume itself may show 10 GB free in Finder, but Photoshop reserves space aggressively and can hit its limit well before the disk reads zero.

Fix 1: Purge Photoshop's Internal Caches Immediately

This is the fastest first step. With Photoshop open:

1. Go to Edit > Purge > All.
2. Confirm the warning. This clears clipboard contents, history states, video cache, and undo data held in RAM and on the scratch disk.

You will lose undo history, so save your document first. After purging, Photoshop releases its scratch allocation and you can often keep working immediately. If the error appears at launch before any document opens, skip to Fix 3.

Fix 2: Lower History States and Cache Settings

Photoshop defaults to 50 history states. Each state can hold megabytes of pixel data for a large document. Reducing this cuts ongoing scratch disk consumption.

1. Open Photoshop > Settings > Performance (macOS menu bar).
2. Set History States to 10 to 20 for most work, or as low as 5 for very large files.
3. Set Cache Levels to 2 if you work on large single-layer documents, or keep it at 4 for compositing.
4. Click OK and restart Photoshop.

These changes take effect on the next launch and meaningfully reduce how much scratch space Photoshop claims.

Fix 3: Delete Orphaned Photoshop Temp Files

When Photoshop crashes or force-quits, it leaves temp files behind. These files are named with the pattern Photoshop Temp followed by a number string and live in your system's temp directory. They are safe to delete when Photoshop is not running.

Quit Photoshop completely, then open Terminal and run:

ls /private/var/folders/**/**/**/ | grep -i "photoshop temp" 2>/dev/null

Because macOS sandboxes temp folders per user, the precise path varies. A more reliable sweep:

find /private/var/folders -name "Photoshop Temp*" -type f 2>/dev/null

Delete any results while Photoshop is closed:

find /private/var/folders -name "Photoshop Temp*" -type f -delete 2>/dev/null

On a machine that has seen several Photoshop crashes, this alone can recover several gigabytes.

Fix 4: Reassign the Scratch Disk to a Different Volume

If your startup disk is genuinely low on space and you have an external drive or a second internal volume with headroom, redirect Photoshop to use it.

1. Hold Command + Option at launch to open the Scratch Disk Preferences dialog before Photoshop loads any documents.
2. Alternatively, open Photoshop > Settings > Scratch Disks while the app is running.
3. Enable a volume with at least 20 GB free and drag it to the top of the list.
4. Uncheck the startup disk if it is critically full.
5. Click OK and restart Photoshop.

Photoshop works best with a scratch disk that has 20 to 40 GB of free space available at all times. An external SSD via USB-C or Thunderbolt works well; a spinning hard drive will be noticeably slower.

Fix 5: Clear the Adobe Application Cache Folders

Adobe applications write caches to ~/Library/Caches/ that survive app updates and can grow large over time. The folders most relevant to scratch disk pressure are:

• ~/Library/Caches/com.adobe.Photoshop
• ~/Library/Caches/Adobe/ (shared Adobe cache, can contain gigabytes of media cache from Premiere and After Effects)

To open your Library folder in Finder, hold Option and click the Go menu, then select Library. Navigate to Caches and delete the Adobe-related subfolders while all Adobe apps are closed. Photoshop will rebuild a fresh cache on next launch.

For the Adobe Media Cache specifically, you can also clear it from inside Premiere Pro or After Effects at Preferences > Media Cache > Clean Database and Cache.

Fix 6: Free Overall SSD Space to Give the Scratch Disk Room

This is the fix that most guides skip past too quickly. Even after purging caches, if your startup disk is below 15 to 20 GB free, Photoshop will keep hitting its limit on large projects. The scratch disk error is often a symptom of general disk saturation rather than anything specific to Photoshop.

Common culprits on a Mac that squeeze SSD space:

• System Data / purgeable files: macOS reports these in System Settings > General > Storage. Optimized storage can park iCloud-eligible files locally longer than expected.
• Old iOS device backups: Check ~/Library/Application Support/MobileSync/Backup/. These are often several gigabytes each.
• Xcode derived data and simulators: ~/Library/Developer/Xcode/DerivedData/ and ~/Library/Developer/CoreSimulator/Caches/ can consume 20 to 60 GB on developer machines.
• Duplicate files and large forgotten downloads: ~/Downloads/ and ~/Documents/ often hold duplicated assets from past projects.

Go through each of these manually or use a disk map to find what is actually taking space before deleting anything. The macOS built-in Storage view (System Settings > General > Storage > Manage) gives a basic breakdown but does not show individual large files inside System Data.

Crumb gives you a full disk map of your startup volume, surfaces large files and folders, and flags app leftovers like orphaned caches and app support data. It runs entirely on-device and needs no account. If your SSD is at 90 percent or above, running a Crumb scan before a big Photoshop session is a practical way to spot and clear what is filling the scratch disk's breathing room.

Fix 7: Increase RAM Allocation to Photoshop

The more RAM Photoshop can use, the less it leans on the scratch disk. On machines with 16 GB or more of RAM, the default allocation is often conservative.

1. Open Photoshop > Settings > Performance.
2. Under Memory Usage, raise the slider to 70 to 80 percent of available RAM. Avoid going above 85 percent or macOS itself will start swapping.
3. Click OK and restart Photoshop.

On an M-series Mac with unified memory, Photoshop manages its memory allocation differently, but the setting still applies. Giving Photoshop more RAM headroom reduces how often it writes to the scratch disk at all.

Preventing the Error from Coming Back

The photoshop scratch disk error mac tends to recur on machines where disk space slowly tightens over months of use. A few habits that help:

• Keep at least 15 to 20 GB free on whichever volume Photoshop uses as its scratch disk.
• Purge Photoshop caches (Edit > Purge > All) before starting large compositing sessions.
• Delete orphaned temp files after any crash before relaunching.
• Review your disk usage every month or two, not just when something breaks.

Reclaiming space proactively, before the error appears, is faster than troubleshooting it mid-project. Crumb's whole-disk map makes it straightforward to see what has accumulated since your last cleanup, so you can clear it in a single pass rather than hunting through folders manually.