Pro Tip: Photoshop Scratch Disk

Many photographers, especially those newer to Photoshop, aren’t familiar with scratch disks. By setting up an external drive (or second internal drive) as a dedicated scratch disk, Photoshop can show significant improvements in performance. Below are the steps outlined by Adobe for setting up a scratch disk. By default the system hard drive is assigned as a scratch disk, but because it’s running the operating system and reading/writing the images (if you’re working from the local drive) it’s not the best option. A dedicated scratch disk is definitely the way to go, and it doesn’t even have to be a large capacity disk.

Assigning scratch disks

When your system does not have enough RAM to perform an operation, Photoshop uses a proprietary virtual memory technology, also called scratch disks. A scratch disk is any drive or drive partition with free memory. By default, Photoshop uses the hard drive on which the operating system is installed as the primary scratch disk.

Photoshop detects and displays all available internal disks in the Preferences panel. Using the Preferences panel, you can enable other scratch disks to be used when the primary disk is full. Your primary scratch disk should be your fastest hard disk; make sure it has plenty of defragmented space available.

The following guidelines can help you assign scratch disks:

  • For best performance, scratch disks should be on a different drive than any large files you are editing.

  • Scratch disks should be on a different drive than the one your operating system uses for virtual memory.

  • RAID disks/disk arrays are good choices for dedicated scratch disk volumes.

  • Drives with scratch disks should be defragmented regularly.

    Change the scratch disk assignment

    1. Do any of the following in the Scratch Disks area of Performance preferences:
      • To change the scratch disk order, click the arrow buttons.

      • To enable or disable a scratch disk, select or deselect the Active checkbox.

      To ensure optimal performance, networked drives are not available as scratch disks.

    2. Click OK.
    3. To apply the changes, restart Photoshop.