I am running 3.8 from an iso image on the harddisk and swap on the harddisk however persistent homedir is not enabled.

According to mount, /UNIONFS is the union of /ramdisk and /KNOPPIX

According to df, the size of /UNIONFS is 6.1G - but /ramdisk is 391M and /KNOPPIX is 1.9G - so where is the other 4G coming from?
Code:
knoppix@1[tmp]$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/root             3.4M   23K  3.4M   1% /
/dev/hda1              28G  4.7G   22G  18% /cdrom2.loop
/cdrom2.loop/knx38.iso
                      695M  695M     0 100% /cdrom/
/dev/cloop            1.9G  1.9G     0 100% /KNOPPIX
/ramdisk              391M  391M     0 100% /ramdisk
/UNIONFS              6.1G  6.1G     0 100% /UNIONFS
Also, when I wrote the large file to /ramdisk that filled it completely, there was considerable disk activity. I am wondering what on the harddisk it would be writing to.