Scratch Disks best choices and considerations

[laoshi Royal]

Scratch Disk Questions

I am a photographer/artist who at times, creates extremely large master files from which I derive numerous print masters. Those master files can have as many as 325 layers and be 180 GB in total size for example, though most are in the 50 to 100 GB range.)

My questions are these. Which of these 3 types of drives are best suited for use as a Photoshop Scratch Disk while working on those extremely large master files: 1) a 2TB SATA III SSD or 2) a 2TB NVMe M.2 Gen 3 SSD (both types of SSDs are mounted in external housings with Thunderbolt 3 connectivity) or 3) a 4TB 7200 rpm HDDs in external housings with USB 3.1 Gen 1 connectivity. All of these drives are connected to a Mac Studio M1 Ultra with 64 GB of RAM.

I am cognizant of the different read/write speeds of the 3 types of drives that I’ve mentioned but, specifically, I am trying to understand things like A) How taxing on the life of a drive is it to utilize it as a “Scratch Disk” and B) how necessary is an extremely fast (or large disk) when it comes to a Scratch Disk in relation to the size of the master files I am working on?

[D Fosse]

The optimal solution, and what you definitely should have had here, is an NVMe plugged directly into an M.2 port in the motherboard. That's the current standard.

If you can't do that, you're limited by the interface more than drive technology.

I'm not going to go into why you need those outlandish files sizes, but at face value you will need several TB of scratch disk space. I'm not at all convinced 2TB is enough.

The scratch file quickly loses sight of the nominal file size. It contains all your history states for all open documents, and if you have smart objects quite a bit of overhead. You could be looking at 50-100 times the file size.

Drive wear is overrated. There is constant read-write to the user account on the system drive even with no user files on it. If drives wore out that quickly we'd hear about it.