What Is a Scratch Disk?

A scratch disk is hard disk space that is temporarily allocated to any given running application to store transitional data. You can think of it as “over-spill” for your RAM. While it depends on the program itself, Photoshop uses the scratch disk to store slices of your documents and history panel. By default, Photoshop uses the same hard drive as the operating system. When you see the “Scratch Disks Are Full” error, this means that the scratch disk you assign is either completely full or (more likely) close to capacity. As such, there are a few methods you can carry out to resolve the issue.

How to Fix the “Scratch Disks Are Full” Error in Photoshop

The below methods are in no particular order and aren’t exclusive to one another. As such, you can jump to any method and start there and even combine it with one of the others on the list.

1. Make Some Room on Your Primary Hard Drive

If your hard disk is full regardless of the reason, the logical approach is to delete some files. In fact, Photoshop will often display the “Scratch Disks Are Full” error, before the hard drive is at 100 percent capacity. This is because it’s optimal to leave around 10 to 20 percent space on your disk regardless of the programs you’re using. In fact, Adobe recommends leaving 20GB free when using Photoshop. This may seem a lot, but your scratch disks often hold portions of projects and history data, so even 20GB can run out fast. There are two approaches to take here make more room:

Delete files from the scratch disk.Move files from the scratch disk to somewhere else.

Regardless of which method you choose, it’s worth noting some typical practices for any work that involves heavy use of the hard disk. This applies to photography, graphic design, music, and other similar tasks:

Use a separate hard drive for system and program files, or at least partition a single drive.Keep a smaller “working” hard drive (or partition) that lets you run a single project. This way, you can migrate the entire project once you’re done.Implement an archiving strategy for your overall work. For example, you may have a partition for one project, storage for current client or school assignments on another partition, and cloud-based storage for old and completed projects.

For macOS users, there is a dedicated Storage Management panel to help win back some free hard drive space. There are a few nice features here, such as the Reduce Clutter section that lets you filter your hard drive in a number of different ways. You can also implement automated optimization, which will only keep the most recent files you use on your computer. Windows has a similar panel: Disk Cleanup. This is a more straightforward panel that lets you see the size of a specific group of folders, then empty them as necessary.

2. Optimize Your Hard Disk Space

You have limited ways to influence the size of your scratch disk within Photoshop, although it’s a useful option to “eke out” small volumes of storage. You can do this through the “Preferences -> File Handling” screen. For macOS, head to “Photoshop -> Preferences -> File Handling” in the top toolbar. For Windows, it’s under “Edit -> Preferences -> File Handling” Here, find the “Automatically Save Recovery Information Every … ” option and choose a longer time. As an alternative, you can turn this off using the checkbox. The drawback here is that you’ll have less protection against an inevitable crash halfway through a project. Even so, it’s one way to keep your drive from filling up and causing the “Scratch Disks Are Full” error. You can also limit the number of history states your system saves. To do this, head to the “Preferences -> Performance” panel. Under the “History & Cache” section, look for the “History States” value. You can change this value here to something lower (or higher if you wish). Of course, lower values will mean using less space to store the information at the risk of having fewer states cached to return to.

3. Specify the Right Scratch Disk in Photoshop

You’ll also want to make sure that you select the right scratch disk for Photoshop. If you implement a system for your hard drives, you’ll need to specify a suitable scratch disk. For example, if you set a scratch disk on your smallest drive, this will fill up fast and bring up errors. However, if you choose another drive with larger storage, you’ll have a myriad of space to store scratch data without ever seeing errors. To do this, you’ll need to hold down keys when you launch Photoshop.

Windows: Control + AltmacOS: Command + Option

You’ll see a Scratch Disk Preferences pane appear. Here, choose a more suitable disk and click OK to save your changes. It’s a good idea to select the fastest drive with the most free space available.

4. Reset Photoshop’s Preferences

If your system is affected by a crash when using Photoshop, this can corrupt your preferences file. In turn, this can affect scratch disk allocation and show the “Scratch Disks Are Full” error. To resolve this, you need a two-pronged attack. First, rest the preferences. There are a couple of ways to do this. The most straightforward is to hold a key combination when you launch Photoshop:

macOS: Command + Option + ShiftWindows: Control + Alt + Shift

This will display a small dialog box asking whether you want to delete the preferences file. You can also use the Preferences screen to delete the file. For macOS, head to “Photoshop -> Preferences -> General,” and for Windows, go to Edit -> Preferences -> General.” Here, select “Reset Preferences on Quit,” then click OK to confirm. You won’t be able to select the option again, and the preference file will regenerate on the next launch. Note that you can reset the preferences manually, too, which is the most “complete” method of doing so according to Adobe. You should quit out of Photoshop before you attempt this, and if you’re on a Mac, look to show your hidden files. Next, head to the following path on your computer.

Windows: “Users/[yourusername]/AppData/Roaming/Adobe/Adobe Photoshop [version]/”macOS: “Users/[yourusername]/Library/Preferences/”

From this location, drag the “Adobe Photoshop [version] Settings” folder to a different location, then open Photoshop. This will reset your preferences, then regenerate the necessary file.

Recommendations to Avoid the “Scratch Disks Are Full” Error

Here are some recommended guidelines for your scratch disk to avoid the dreaded error:

Use a drive that’s fast (i.e. with good read/write speeds) and with plenty of space.A Solid State Drive (SSD) is a better fit as a scratch disk over a mechanical drive.Look to host your scratch disk on a different drive than the one your OS uses for virtual memory and any large files you edit.

Also, you may want to put a regular defragmenting strategy in place for your hard disks, as this will help improve performance.

1. How much free space do I need to avoid the “Scratch Disks Are Full” error?

Adobe recommends this simple rule to determine how much disk space on a scratch disk is necessary: if working on a complex project, you’ll need as many times the project file size as there are history states. For example, if the file you’re working on is 300MB and you’d like to have 50 history states, then you’ll need 15GB free on your scratch disk.

2. Can I use any hard drive for my scratch disk?

No, you can’t use any hard drive. Adobe doesn’t recommend thumb drives, USB2 drives, or NTFS-formatted drives on macOS. If using external drives, you’ll also want to make sure you plug the drive in to a suitable port with the right level of bandwidth for your drive:

Thunderbolt: 10GB/seceSATA: 600MB/secPCIe: 500MB/secUSB3: 400MB/sec

Mac drives should use the macOS Extended format, and Windows should use NTFS, exFAT, and FAT32 drives.

In Summary

Your hard disks are on the front line when it comes to using resource-heavy apps such as Photoshop. Because of this, you want to make sure your hard drive is up to the task. Read on to learn more about drives, specifically, SSD vs. HDD vs. USB flash drives.