Just finished compiling 6.2RELEASE after having a small problem.
buildworld and buildkernel went fine but installkernel crapped out at
some module because the root filesystem was full. My root is just the
way I like it; 128MB, and I've never had this issue before. Even when I
ran 4.x with an 80MB root partition, build sequences completed fine.

The issue was initially not space per se but inodes. There was a little
space left on / but the inodes were used up. I discovered that
/root/.ccache had a ton of files in it. Deleted that, created
/tmp/.ccache and linked to it from /root. All went well after that,
with /tmp/.ccache being 103MB and 5301 files at compile's end.