Temporary files filling C drive, preventing work on large project

[sam_marrs]

I have a nearly full primary drive in my computer, with not enough space for some of the projects I'm working on. To counter this, I've bought a 4TB sdd and have moved both the photoshop installation and the scratch drive to that larger drive. Despite the abundant space on the new drive (> 2TB), photoshop still writes temporary files to the C drive. Those temparary files completely fill up the remaining space and prevent any work from being done. How do I configure photoshop to write temp files to another drive?

My prior search of the community suggests that this is not possible, so I'm tagging this as a bug due to it preventing work.

Any help would be appriciated.

Photoshop version:  25.11.0 20240716.r.706 b326a7d

OS: Windows 10

Steps to reproduce: 

1. Change scratch drive to something other than the primary OS drive. 
2. Load files into stack (I currently fail at 150 photos selected, ~150mb each when decompressed)
3.  Create smart object from all layers
4.  Watch the available space of your primary drive increase as the smart object is created.
5.  Change stack mode to mean (it is this step where I run out of space and the command fails)

Expected result: All temporary files are writen to a configurable drive. 

Actual result: primary drive fills up despite being different than the selected scratch drive

[AxelMatt]

You can configue the Scratch Disks in the PS preferences.

[D Fosse]

Not a bug, but maybe a feature request. This is by design, for some technical reason above my paygrade.

Smart objects are always stored in the system TEMP directory while they are edited and processed. They are not stored in the scratch file. Note that the distinction here is between the master file and the embedded smart object file.

This was explained some time ago by a Photoshop engineer, but I can't locate it now. I do remember it.

You solve the problem by having more space on the system drive. And I have to say, if you're routinely mashing 150 big raw files into one smart object, you should expect that you need ample computer resources to handle it. This is not your ordinary everyday workflow.

[sam_marrs]

Untracked landscape astrophotography tends to have a large number of photos. Stacking the ground to reduce noise in more dedicated astro software is possible, but none I've tried produce results as good as a mean or median stack in Photoshop.