Speed Up Photoshop on Mac: Scratch Disks, Storage & the Setting People Miss
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
- 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
- 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
Follow these steps carefully.
- 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
- You are using an older Mac
What kind of drive works best
- External SSD, not a traditional hard drive
- Connected via USB‑C or Thunderbolt
- Formatted for macOS
Avoid using:
- Network drives
- NAS devices
- 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 is 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
- 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
- Avoid heavy cloud syncing during large edits
This gives Photoshop priority access to system resources.
What “Scratch Disk Full” really means
This error does not mean Photoshop is broken.
It means:
- Photoshop has run out of temporary working space
Common fixes include:
- Freeing up storage
- Changing scratch disk priority
- 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
- 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
- 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
- Ongoing Mac support across Melbourne
