Please help! FCPX crashes system by background rendering

I upgraded to FCPX 10.3.3 today it wanted to do a bunch of back ground rendering on the library. That's fine, except it used more and more memory 40GB+ and then also started created more and more swap. Eventually I run out of disk space and the system just crash.

Any ideas how to stop or fix this?

I'm running latest version of macOS.

Where is the library and where is the cache located? How much free space on the system drive?

The library is in external drive. The cache is in the library.

50GB free on the system drive. But eventually it runs out

Something doesn't sound right. First switch off background rendering and then deleted generated files for the library.

Something doesn't sound right. First switch off background rendering and then deleted generated files for the library.

ok thanks let me try that, but then what do I do afterwards? Start rendering back up again?

50GB is not much, your system drive (let's say it is a 1TB drive) is more than full. Like Tom said, clear the render files. Why is your system drive so full, especially when the Library is on an external drive?

My main disk only has 250GB, it is a mac pro. So how much disk space is it suppose to have for rendering? I don't understand why it can't use the external drive for the working space and it has to write 50GB+ worth of memory space to do the work? Doesn't make sense

Here's what I tried.

I rolled back to my old library via time machine. Then used version 10.2 to delete all render files, deleted all plugins and resetted the preferences.

Then I upgraded to 10.3 again. It failed same as last time

Why are you rendering? Do you really need to? Can you post a screenshot of your library properties.