Oracle Critical Patch Update and disk space

I'm about to install the latest Critical Patch Update (CPU) on a Solaris LDOM
with limited disk space.  From my review of the installpatchset script, it
looks like the script does do a space verification, but I just wanted to make
sure.  Does the CPU install script execute a space check before it starts
installing the patches?  How about before installing the prerequisites?

Any thoughts on a rough idea on how much disk space is too little?  This
particular system only has about 800 MB free at root, and the /var, /usr and
/opt partitions are all part of the root filesystem.  Thank you.

Gene Beaird,
Pearland, Texas