internal hard drive does not show up in scratch disc

[caligula1]

Hi, I'm on an iMac. retina 5k 27 inch late 2015, processor 4GHz intel core i7, memory 32 GB, startup disk Mac HD Graphics AMD Radeon R9 M395X 4096 MB. I upgraded to Mohave, but started having problems with performance lag, occasional crashes, free transform acting very slowly, difficulty changing the opacity of the layer  I was free transforming  to a lower opacity to view layer underneath so the free transform would match up with the layers below precisely, etc. My typical file size is about 1 to 2 GB as I  work on images a long time. Plenty of storage on this mac as the internal hard drive is 1T and only about a third full, plus there are additional external hard drives for photoshop to draw from as scratch discs that have about 10 T of available storage.

As I am kind of old school and don't use many of the new features in each new release of photoshop, I figured I would just use an earlier version of photoshop for the time being like CC15.5 or CC17 in which the AMD Radeon R9 M395X 4096 MB graphics card was supported, but was still having the same performance problems. I checked in photoshop preferences and saw that the internal hard drive was no longer listed as a scratch disk, only the external hard drives in CC15.5 and CC17. That meant  I was stuck using either CC18 or CC19 where the internal hard drive was listed in scratch disks even though the graphics card was no longer supported.

Thinking that  I could use an older version of PS like CC15.5 or CC17 in which my graphics card was supported,  I reverted the system back to high sierra, but still the internal hard drive did not appear in scratch disks for either of those versions. The internal hard drive only appears in CC18 or CC19 in high sierra as well as mohave.

I just want this computer to last until apple releases a new iMac Pro or mac pro, hopefully this year. I learned my lesson about buying a slightly old iMac when I bought this iMac late 2015 in mid 2016, that the graphics card probably won't be supported in photoshop in 2 or 3 years so want to wait for apple to release a new model before I spend thousands of dollars.

The problem wouldn't be so bad if I could add an eGPU with a video card that is supported in CC19, but eGPU's aren't supported with thunderbolt 2 connections which is the type of connection that late 2015 iMacs have.

Does anyone have any suggestions for getting better performance out of a late 2015 iMac with a video card that is unsupported?

It seems like I may as well upgrade the system back to mohave since high sierra also doesn't recognize the internal hard drive as a  scratch disk in pre CC18 versions of photoshop.  What are your thoughts and do you think facing the performance issues I am facing because of the unsupported video card, I am better off keeping the os as high sierra?

Thanks.

[Daniel E Lane]

First, check to see if you have the latest drivers for your video card. That can make a huge difference, especially with that particular card.

Also, You need to check a few things to see what is running how, so...

Go to your preferences and into Performance. Check to see if you are using the Graphics Processor or not. You can try turning that off or on depending on where it is.

Right under that, click the Advanced Settings...

See what is on in there. You may need to turn off the 30 bit display to get it to work right. The retina iMac 2015 does support 10 bit/channel, but there may be driver code issues. Worth checking...

[caligula1]

I checked AMD's website and all the drivers for R9 M395X are for windows. My experience using macs is that the drivers for most  3rd party products are usually included in the mac OS. The only 3rd party drivers I've ever had to install are for my wacom tablet. I've tried unchecking 'Use Graphics Processing' and it just seemed to make things slower. I currently have under 'advanced graphics'  checkmarks next to 'use graphic processor to accelerate computation' and 'use open GL. I also have a checkmark next to 'use native operating system GPU acceleration'. Un-checked are ' antialias  guides and paths' and no check-mark next to 30 bit display.

[Daniel E Lane]

ok, so if your card is unsupported, we may have to figure out how to not use it for processing the important stuff to help speed everything up. Get it off the card and onto the CPU. Try turning off the OpenGL and see if that helps.

[caligula1]

will have to play around with all the options in performance such as turning off Open GL and see if that makes any difference. I looked at your profile and saw that you are on an iMac too .Out of curiosity what model iMac are you using? Must be later than my late 2015 iMac.

I am also wondering why photoshop can't see the internal hard drive in versions of photoshop before CC18 which means I can't use it as a scratch disk in high sierra or mojave?  Because I am kind of old school in the way I work, I don't really need to be on the latest version of photoshop as I tend to do things the way I've always done them from around CS 3, 4 or 5 and not use new tools so could easily use an earlier version of photoshop in which my video card was still supported, except for the scratch disk problem.  I'm also wondering if upgrading from high sierra to mohave would result in any improvement in performance in photoshop CC18 or 19?

[Jeff Arola]

The reason older photoshop cc versions don't show your startup disk in the scratch disk preferences is

your drive is formatted using the new Apple File System (APFS). The startup APFS drive is still being used

as a scratch disk or photoshop would not start if that was the only drive you had, however, that would be a

problem if you wanted to use another internal drive or external drive formatted in APFS a scratch disk.

Adobe fixed not being able to show APFS formatted drives in cc 2018.

Is your internal 1TB drive an ssd?

[caligula1]

Jeff, I believe the the 1Tb internal hard drive is a ssd.

[caligula1]

Would it make any difference in terms of photoshop's performance if I were to upgrade from high sierra to mojave or am I better off staying in high sierra given that my graphics card is no longer supported?

The only reason i downgraded from mojave to high sierra was that I thought that in high sierra my internal hard drive would be recognized as a scratch disk in older, pre CC18 versions of photoshop in which my graphics card was still supported by Adobe, but like I said in an earlier post, the internal hard drive is not recognized in versions of photoshop prior to CC18.