To add an external hard drive as a scratch disk in Photoshop, connect the drive to your computer, enable it in Scratch Disks preferences, and restart Photoshop. This setup offloads temporary file storage from your internal drive, directly addressing performance slowdowns and "scratch disk full" errors.
Add an external hard drive as a scratch disk in Photoshop: The three verified steps
- Connect the external hard drive to your computer using a USB or Thunderbolt cable. Ensure the drive is powered on (if required) and appears in your file explorer.
- In Photoshop, go to Edit > Preferences > Scratch Disks. Check the box next to your external drive in the list. Drag it to the top of the list to set it as the primary scratch disk, then click OK.
- Restart Photoshop completely. The changes only take effect after a full restart. To verify, open the Scratch Disks preferences again, the external drive should show as active.
Before you start
Back up any important data on the external hard drive before using it as a scratch disk, because Photoshop may overwrite existing files. The drive must use a compatible file system: exFAT works across both Windows and Mac, while macOS requires Mac OS Extended (Journaled) and Windows works with NTFS. Always safely eject the drive after closing Photoshop to prevent data corruption.
Connect your external hard drive
Physically connect the drive via USB 3.0, USB-C, or Thunderbolt for the best transfer speeds. After connecting, confirm the drive appears in your operating system's file explorer (Finder on Mac, File Explorer on Windows). A stable connection during Photoshop use is critical, if the drive disconnects mid-session, you risk losing unsaved work or corrupting temporary files.
Configure scratch disk preferences in Photoshop
Navigate to Edit > Preferences > Scratch Disks (Windows) or Photoshop > Preferences > Scratch Disks (Mac). In the list of available drives, check the box for your external hard drive. You can reorder the priority by dragging drives up or down, Photoshop uses the top drive first. Click OK to save the selection. If you need to free up space on that drive first, you can install genshin impact on external hard drive to relocate large games. Do not adjust cache levels or tile sizes unless you understand their impact; the default settings work for most users.
Restart Photoshop to apply changes
You must restart Photoshop after changing scratch disk settings. Simply closing and reopening the application is sufficient. To verify the new scratch disk is active, reopen the Scratch Disks preferences, your external drive should appear with a checkmark and be listed first. You can also check the drive's activity light during heavy Photoshop operations to confirm it's being used.
Troubleshooting common issues
Drive not appearing in the list
If your external drive does not show up in the Scratch Disks preferences, first confirm it is properly connected and visible in your file explorer. The drive must be formatted with a compatible file system, drives formatted as FAT32 may not appear. Try a different USB port or cable. On macOS, check that the drive is mounted and not set to "ignore ownership" in Finder's Get Info panel.
'Scratch disk full' errors persisting
If you still see "scratch disk full" errors after adding an external drive, the issue is likely that Photoshop is still using your internal drive as the primary scratch disk. Go back to Scratch Disks preferences and ensure your external drive is checked and listed above your internal drive. Also, free up space on the external drive, Photoshop needs at least 10-15% free space to operate efficiently. If you want to avoid the risk of data loss, consider using a dedicated drive for scratch files only.
Performance expectations when using external versus internal drives
For best results, use a USB 3.0 or Thunderbolt connection with a solid-state external drive. If you need to work on complex PSD files with many layers, an external SSD can provide a noticeable improvement over a nearly full internal HDD. However, if your internal drive is already a fast SSD with plenty of free space, adding an external scratch disk may not yield significant gains. If you want to maximize the lifespan of your external drive, avoid using it for both scratch files and active project storage simultaneously.
