When it comes to using Photoshop the weakest link in your computer setup is your hard drive unless you are using a higher transfer speed solid state drive (SSD) such as a Corsair Neutron or Crucial M4 series drives. These drives are 600%+ faster at reading and writing data than your standard disk based hard drive plus with a much lower latency. This translates to a much more responsive feel when using Photoshop and more stable.
You can never have enough free space
However even though speed is important never for get about space. Yes solid state drives are expensive per gigabyte but don’t skimp on space when it comes to using Photoshop especially if it is for a laptop. For the first time I recently filled up my separate 128GB SSD scratch drive putting together a composite of about 40 images and not even close to a final with no other Photoshop documents open and here is the interesting part. The file saved was only 2.7GB. With each image being 16 bit and being placed as a smart object Photoshop used up scratch disk space at a rate of about 1.1GB for each file added, despite the saved tiff file only being around 100MB, and around 900MB per movement/re-size of an object.
I do realize not everyone is doing this kind of massive composite work but with camera sensor sizes getting even larger and working with smart objects never underestimate the importance of more than enough scratch disk space and the need for SSD drives in your work station computer. The drive Windows 8 is installed on with software and minimal files is another 128GB SSD and only has 38GB free. I wouldn’t have even been able to add all of the files as smart objects or open the file once added had I not had the extra scratch drive.
It is also worth noting that when working on a large file like this in Photoshop; if you have multiple drives listed as scratch disks Photoshop can only use one drive per file. So if I had multiple drives with 38GB of free space each that wouldn’t have helped any. The only solution is a single drive with enough free space.
Photoshop Scratch Disk Full Error
Once I filled up the scratch disk I got an error that said “… scratch disks are full”. Some times when this happens you also may not be able to save the file either which creates a frustrating situation. However there is a simple solution. First if you are working on a file and you might run into this issue turn down the number of history states by going to Edit > Preferences > Performance and turn down the ‘History States’ by 20-50%. (Save documents and restart Photoshop to apply settings) to avoid the situation all together.
Clear Scratch Disk Space
To clear out the space used on your scratch disks by previous history states you can go to Edit > Purge > All. Once you click OK on the warning box you will have cleared out all previous history states and clipboard copies and should free up some scratch disk space. However this is not a long term fix as you will never recover the amount of space as if you just open the file but should allow you to save the file and maybe continue working.