Comment 3 for bug 1427164

I'm not sure how this could be happening.
curtin's swap logic is http://bazaar.launchpad.net/~curtin-dev/curtin/trunk/view/head:/curtin/swap.py#L44 .

It generally tries to keep the swap file of sane size by default.

Could you run this on the system and collect the output:
$ path=/
$ python -c 'import os, sys; s = os.statvfs(sys.argv[1]); print("%s / %s" % (s.f_frsize * s.f_blocks, s.f_frsize * s.f_bfree))' "$path"
$ df -k

where 'path' is the path to the mounted 100G filesystem that is mentioned.
Also, the installer log from maas attached would be nice.