Avid Running Low on Disc Space During Large Export

While doing a very large Avid export (over 3 hours of video) to an external drive, Avid tells me that I am running low on internal disc space.  I made sure that all the renders would be going to the external drive, as well as the file export itself.  I looked on the internal disc, there was no AvidMedia Files folder, but the disc now had less than a GB in free space even though before the export there had been around 10 GB.  Why is this?

I'm using a HPz400 with 12 GB RAM.

Thanks

Jack