Mac error code 189 on external HDD

I am trying to move my apps onto it as my other HDD says its lack of space also.

 

By @Royal history

Don't do that! That's the wrong way to go about it. An application is only a couple of GB at most. That's insignificant and nothing in the big picture. You'll get the same problem in two weeks.

Installing applications on other non-system drives can cause other problems - and in any case, a large part of the application will be in your user account, on the system drive, anyway.

There's no way around it. You need to clear out space on your system drive. If you're already getting warnings that it's almost full, you're in a hurry. You can soon get into bigger problems than Photoshop.

What really needs disk space with Photoshop is not the installation files, but the scratch disk. Raster image editing requires huge amounts of memory, much more than any RAM you may have installed. So temporary working data are written to disk, aka the scratch disk. For most normal use, you should have at least 200GB or so free space for the scratch disk, sometimes more.

Your user account is most likely full of junk you don't need. All your applications will dump all kinds of stuff there, and much of it is never removed again. Start by doing a disk cleanup in your operating system. That can sometimes be surprisingly effective. Then I'd recommend a more systematic approach. There should be a Mac equivalent to the Windows utility WinDirStat, can't remember what it's called - but it will show you exactly what fills up your drive and where it is.

Here's how WinDirStat looks in Windows:

@Royal history I'd imagine you need to free up space on your main drive that the OS resides on, you can't just move apps to an external drive and installing on an external drive is not recommended