Speed Up Photoshop on Mac: Scratch Disks, Storage & the Setting People Miss
Photoshop slow or showing scratch disk full on your Mac? Learn how scratch disks and free storage affect speed, and the one setting to change.
If Photoshop feels slow on your Mac, freezes, or shows “scratch disk full” errors, the problem is usually storage, not Photoshop itself. This guide explains scratch disks, storage setup, and the one setting that makes the biggest difference to performance.
Why Photoshop slows down on a Mac
Photoshop is one of the most demanding apps you can run on macOS. Even on a fast Mac, performance problems usually appear when available storage is low, Photoshop runs out of memory, or temporary working files have nowhere to go. When this happens, Photoshop relies heavily on something called a scratch disk.
What a scratch disk is (in simple terms)
A scratch disk is temporary working space that Photoshop uses when it needs more memory than your Mac can provide. You can think of it as extra breathing room for Photoshop, space for large edits, undo history, previews and effects, essential when working with large images or many layers. On a Mac, scratch disks use storage space, not RAM.
Where Photoshop gets scratch disk space by default
By default, Photoshop uses your Mac’s internal drive. This works well only if there is plenty of free space. If your internal drive is nearly full, Photoshop slows down, files take longer to open or save, “scratch disk full” errors appear, and the app may refuse to open at all.
How much free storage Photoshop actually needs
A very common mistake is thinking a few gigabytes of free space is enough. For smooth, reliable performance, keep at least 20 to 30 GB free, more if working with large photos, complex designs, or many layers. This free space is not optional for Photoshop.
The one setting most people miss
This single setting fixes more Photoshop performance issues than almost anything else.
Scratch Disk Priority. Photoshop allows you to choose which drive it uses first for scratch disk space. Most people never change this setting. If the fastest or emptiest drive is not first in the list, Photoshop will slow down unnecessarily.
How to set the correct scratch disk on macOS
- Open Photoshop
- Click Photoshop in the menu bar
- Select Settings
- Click Scratch Disks
- Make sure the fastest drive with the most free space is ticked
- Drag that drive to the top of the list
- Click OK
- Restart Photoshop
This change alone often results in an immediate speed improvement.
Using an external drive as a scratch disk
An external drive can dramatically improve performance, especially on Macs with limited internal storage. This works particularly well when internal storage is nearly full, files are very large, or you’re using an older Mac.
What kind of drive works best: an external SSD, not a traditional hard drive, connected via USB-C or Thunderbolt, and formatted for macOS. Avoid network drives, NAS devices, or slow USB hard drives, scratch disks must be fast and local.
Keep your Mac’s storage healthy
Scratch disks rely on free space to work properly. If your Mac is nearly full, Photoshop will struggle no matter how it’s configured. Simple storage habits that help: keep at least 20 percent of your drive free, move old projects to external storage, empty the Trash regularly, and avoid working directly from Desktop or Downloads. Good storage habits improve performance across the entire Mac.
Close memory-heavy apps before using Photoshop
Photoshop competes with other apps for memory and storage access. Before starting a Photoshop session: quit web browsers with many tabs, close video or design apps not in use, and avoid heavy cloud syncing during large edits. This gives Photoshop priority access to system resources.
What “Scratch Disk Full” really means
This error doesn’t mean Photoshop is broken. It means Photoshop has run out of temporary working space. Common fixes include freeing up storage, changing scratch disk priority, or adding a fast external SSD.
When hardware upgrades make a difference
Scratch disk tuning goes a long way, but there are limits. Consider hardware upgrades when files are extremely large, projects involve hundreds of layers, or Photoshop is used alongside video or 3D apps. On Apple silicon Macs, more memory significantly improves performance for creative work.
Summary
If Photoshop feels slow on a Mac, the cause is almost always storage or scratch disk configuration. To speed things up: keep plenty of free storage, set the correct scratch disk priority, use a fast external SSD if needed, and close other heavy apps before editing. That one scratch disk setting is often the difference between frustration and smooth performance.
Need help speeding up Adobe apps on your Mac?
If Photoshop is still slow, or if you want help setting up scratch disks, storage, or backups for creative work, contact Your Mac Tech. We can help with Photoshop and Creative Cloud optimisation on macOS, external SSD and storage setup, backup planning for creative files, and ongoing Mac support across Melbourne. If you run a creative or design business specifically, see our Creative & Design Businesses industry page, or our Business Software & Cloud Services page for broader software support.
