Configure Secondary Scratch Disks in Photoshop

When working with large, multi-layered files in Adobe Photoshop, your primary storage drive can quickly run out of temporary space, triggering the "Scratch disk is full" error. Configuring secondary scratch disks allows Photoshop to seamlessly roll over its temporary cache to additional internal or external drives when your main drive reaches capacity. This guide explains how to designate and prioritize backup scratch disks to maintain system performance and prevent crashes.

How to Access Scratch Disk Preferences

To configure multiple scratch disks, open the Scratch Disks manager inside Photoshop:

  • On Windows: Click Edit > Preferences > Scratch Disks.
  • On macOS: Click Photoshop > Settings (or Preferences) > Scratch Disks.

Enabling Secondary Drives

Once the Scratch Disks preferences window is open, you will see a list of all local storage drives connected to your computer, alongside their free space and file system format:

  1. Locate the drives you want to use as backup storage.
  2. Check the box in the Active column next to each secondary drive you want Photoshop to use.
  3. Click OK to save the changes.
  4. Restart Photoshop to ensure the new storage configuration takes effect properly.

Setting Drive Priority

Photoshop writes temporary data to drives based strictly on the priority order listed in the Scratch Disks menu. When the top drive runs out of room, Photoshop automatically spills the remaining data onto the next designated drive.

To set the fallback order:

  1. Select a drive in the list.
  2. Use the Up Arrow and Down Arrow buttons on the right side of the dialog box to change its position.
  3. Ensure your fastest drive (such as an internal NVMe SSD) is at the top of the list as the primary drive.
  4. Place secondary SSDs or high-capacity mechanical drives below the primary drive in descending order of speed.

Best Practices for Secondary Scratch Disks

  • Use Fast Connections: Secondary drives should ideally be internal SSDs or external drives connected via high-speed interfaces like Thunderbolt or USB 3.2.
  • Avoid Removable Media: Do not use slow USB flash drives, memory cards, or network-attached storage (NAS) drives, as Photoshop does not reliably support them for scratch disk allocation.
  • Maintain Dedicated Free Space: Ensure secondary drives have at least 50 GB to 100 GB of free space, especially when working with high-resolution documents, 3D assets, or complex smart objects.
  • Keep Drives Connected: If an external drive configured as a scratch disk is disconnected while Photoshop is running, the application may freeze or crash when attempting to write overflow data to it.