I'm trying to resize a 640x1096 psd file that contains about 20 layers. Photoshop is already taking about 1GB with its scratch disks even though I only have this file open. If I try to increase the canvas space. I get scratch disks full error and have to free up more space on my drive. I got 16gb ram and about 1.5gb free disk space. Why does photoshop need so much scratch disk space for such a simple operation when I have a lot of free ram?
Realistically the solution is to free up a reasonable amount of space on the scratch disk (which doesn't have to be your primary drive, often putting it on a secondary drive yields better performance) - with only 1.5GB of free space on the scratch disk, seeing that error isn't surprising.
Personally, I always maintained at least 10GB free on my scratch disk to minimize issues.
If Photoshop says the scratch disk is full and you have plenty of free space on your computer: If you're trying to crop an image in Photoshop, make sure it's in PIXELS and not inches, that could be a quick problem fix! See this solution: