Performance problem in Cubase Artist 6

When playing back a project, I’ve been getting frequent dropouts. While I’m playing back the song, one or several tracks will stop playing for a period of time. There are also glitches where the playback stops and starts and/or I get a static sound.

While troubleshooting, I discovered that, while I’m playing a song, my disk space usage hits 100% at times. That seems to coincide with the performance problems.

The thing is that, when I’m not running Cubase, my disk has 700 GB of free space. Why is Cubase taking up so much space and how can I fix it?

One song I’m working on has 5 audio tracks and 17 MIDI tracks. 10 of the MIDI tracks are from a dissolved drum track. The audio tracks have 2-4 plugins each. There are also 4 group tracks with one plugin each and 2 plugins on the mix bus.