You’re three hours into a retouch, you add one more layer, and Photoshop stops: “Could not complete your request because the scratch disks are full.” Or it won’t open at all. Both have the same cause. Photoshop wanted more room than the drive had, and usually on the wrong drive. Below is Adobe’s fix list in Adobe’s order, then the part Adobe leaves out: which drive to put scratch on so the error stops coming back.
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TLDR
Adobe’s current page says to free at least 100GB on the drive Photoshop uses as its primary scratch disk. On Windows, delete the files on C: that begin with “Photoshop Temp”. Then restart. If the drive can’t give you 100GB, open Preferences > Scratch Disks and move scratch to a drive that can. On a desktop that drive is a 2TB NVMe SSD. The one I’d give the job to is the Samsung 990 Pro 2TB ($389.99). On a Mac or laptop, keep scratch on the internal SSD and move the files that fill it, your RAW originals and old exports, out to an external drive instead.
What the error means
Photoshop holds the document you’re working on in memory, and a document is much bigger than its file. A 45-megapixel RAW opens as a flat 16-bit image of around 270MB, every layer you add is another copy of whatever that layer covers, and every history state is a snapshot it can roll back to. When all of that outgrows the RAM Photoshop is allowed to use, it writes the overflow to a drive and calls that drive the scratch disk. By default the scratch disk is your boot drive, the same drive that holds macOS or Windows, every app you own, and most people’s Downloads folder.
So the error means one of two things. Either the boot drive is out of room, which is a cleanup. Or your documents outgrow it every week, which is a hardware decision. The hardware fix is the one that keeps you from reading this post again in March.
The fix, in Adobe’s order
These are the steps from Adobe’s troubleshoot scratch disk full errors page, last updated February 23, 2026, with Adobe’s wording where the wording matters. Work down the list. Most people are done after the first one.
1. Free up at least 100GB on the scratch drive
Adobe’s line is “Free up at least 100 GB of space on your primary scratch disk drive.” The 50GB and 20GB figures still in the search results come from older versions of that advice. On Windows, the instruction is to find and delete the files beginning with “Photoshop Temp” on the C: drive. On macOS, Adobe’s advice is to clean up Macintosh HD or move files off to an external drive. Then restart Photoshop, because the temp files it had open stay in use until you do.
On a photographer’s machine the 100GB usually went to the same three places: the Lightroom previews folder, exports you’ve already delivered, and camera cards you copied to the desktop “for now” a year ago. Moving the originals to an external drive is the cleanup that sticks, and the Mac for photo editing guide has the full version of that split.
2. Add a second scratch disk, or move it
If the boot drive can’t give up 100GB, point Photoshop somewhere else. In Preferences > Scratch Disks you can tick more than one drive, and Photoshop spills to the next one when the first fills. Adobe’s page lists the formats it accepts: APFS and macOS Extended (Journaled) on a Mac, NTFS, exFAT and FAT32 on Windows. Adobe recommends an internal SSD, and I’d go one further and make it a dedicated one; the drive section below explains why.
A spinning hard drive or a cheap USB stick clears the error and then makes every brush stroke on a big document wait on that drive. Pick the fastest drive you have with room on it.
3. When Photoshop won’t open at all
The worst version of this error is the one where Photoshop quits during launch. Hold Cmd+Option on a Mac, or Ctrl+Alt on Windows, while Photoshop starts, and it opens the Scratch Disk Preferences dialog before it loads anything else. Pick a drive with room, let it finish launching, then go back and do step 1 on the drive it was using before.
4. Shrink what Photoshop writes
Two preferences decide how much scratch a session eats. History States, under Performance > History & Cache, defaults to 50, and on a layered document each state is another slice of scratch. Adobe’s page says to reduce it. Twenty covers most retouching. The page also names Automatically Save Recovery Information, under File Handling, as the setting to look at when your files are very large, because the recovery copy is one more thing being written while you work.
While you’re in Performance, check Memory Usage. That slider sets how much of your RAM Photoshop is allowed to take before it goes to the drive. Raise it if Photoshop is the only heavy app you run; with Lightroom open alongside, leave it where it is.
5. Purge
Edit > Purge > All clears the undo buffer, the clipboard, the history states and the video cache in one go, and hands back the scratch they were holding without a restart. It can’t be undone, so finish the step you’re on first.
6. Reset the preferences
If the scratch disk setting itself has gone wrong (a drive you removed is still ticked, say), Adobe’s last step is a preferences reset. On a Mac, hold Shift+Option+Command while Photoshop launches and answer Yes when it asks to delete the settings file; on Windows the combination is Shift+Alt+Ctrl. Photoshop starts with factory settings, so you’ll set the scratch disks, and everything else you’ve customised, again.
When the drive is the problem
A 512GB boot drive holding macOS, both Adobe apps, a catalogue and a few years of photos will run short of 100GB again. Adobe’s page says nothing about drives or memory, so from here on it’s my call.
RAM first, because scratch is what RAM runs out into
The Efficiency readout at the bottom of the document window tells you how much of the time Photoshop is working from memory instead of the drive. If it drops during ordinary work, every drive fix is treating a symptom. The numbers I’d buy are in the FAQ of our best PC for photo editing guide. For a full-frame catalogue with both apps open, that’s 32GB. For 100-megapixel files, panoramas and 16-bit layered retouching, it’s 64GB. On a PC the kit I point people at is the Corsair Vengeance RS 32GB (2x16GB). It’s $484.99, and the how much RAM guide explains why 32GB costs that this year. On a Mac the memory is fixed at checkout, which is why the Mac guide ranks the 24GB mini above the 16GB one.
Desktop: a dedicated NVMe drive for scratch and the catalogue
On a tower this is a $390 problem. The Samsung 990 Pro 2TB is the drive for it. It’s $389.99, against a $640 list. It’s a PCIe 4 drive rated to 7,450MB/s, and at 2TB, keeping 100GB free stops being a question. Put the Lightroom catalogue and previews on it too, point scratch at it, and leave the boot drive to the OS and apps. That’s the layout in both AM5 builds in the PC guide, and it’s the same cache-drive role the 990 Pro fills in the internal NVMe roles post for video.
The downside is the slot. You need a free M.2 socket, and on a prebuilt the second one is sometimes under the graphics card. If the board has a CPU-attached PCIe 5 slot, there’s the Samsung 9100 Pro 2TB. It’s $399.95, ten dollars more. The PC guide spends that ten dollars on the scratch drive in the Z890 studio build. For Photoshop alone the 990 Pro is plenty; for a machine that also cuts video, my internal NVMe drives for editing post has the Gen4 versus Gen5 call.
Mac and laptop: free the internal drive, keep scratch inside
A Mac has no second slot, so the fix runs the other way. Keep scratch on the internal SSD, which is the fastest drive the machine has, and move the bulk out: the originals and the finished exports. That’s the split from the Mac guide, and it’s what lets a 512GB mini hold 100GB free. The external drive for the originals is the Samsung T9 2TB. It’s $434.99, near its $490 list. The T7 vs T7 Shield vs T9 post has the comparison against the cheaper T7s.
Using that external as the scratch disk itself is the last resort, for a 256GB machine that can’t hold 100GB free even after the cleanup. Adobe allows it on an exFAT or APFS drive, but a USB cable is a worse home for scratch than the internal SSD, and a knocked cable mid-save is a bad day. If the T9 is already doing scratch duty on a 256GB mini, the next machine needs the bigger drive.
FAQ
Photoshop says the scratch disk is full but the drive has space. Why?
Check which drive is ticked in Preferences > Scratch Disks; the full one is often not the one you’re looking at. A few gigabytes free is the problem itself, since Adobe asks for 100GB. The other case is the document. A new file set up in inches at print resolution is enormous in pixels. Take 24 by 36 inches at 300 ppi. That’s 7,200 by 10,800 pixels, 78 megapixels flat, before a single layer. Photoshop needs scratch for all of it the moment you create the file.
Will more RAM stop the error?
It makes the error rarer, but Adobe still wants 100GB free however much RAM you have, so clear the drive for the error and buy the RAM for speed.
Is the scratch disk the same as the Lightroom cache?
No. Lightroom has its own Camera Raw cache and previews, set in its own preferences, though both want the same fast drive. Lightroom’s slowdowns get their own post here later this month. Resolve editors have the same conversation about the render cache in the Resolve file locations post.
And that’s it
Free 100GB and restart, and you’re working again tonight. To keep it that way, give scratch a 2TB NVMe of its own on a desktop, or move the originals off the internal drive on a Mac, so the 100GB is always there. The steps are Adobe’s, dated February 23, 2026; the drive picks are mine.
