mmc: still there? you asked how to get a file into the bottom 8G of the fs it is probably possible to do this without any special tools, if you are lucky
xfs splits the disk into allocation groups, default size of 1 or 2 Gbytes, you need to get a file into the bottom few allocation groups by default, the allocator puts a new directory in a different group than its parent, and a new file in the same group as its parent. File space tries to stay close to the inode
if you look at xfs inode numbers in hex, they have the allocation group encoded into them
so make a few directories and pick the ones with the lowest inode numbers copy your file into this dir
you can use xfs_bmap to look at the extents of the file and see if you made it this may all fail if the first few allocation groups are full
mmc: yes, i've made a test program to test all blocks output from xfs_bmap for a file.
try the directory trick, you can move the file to where you want after you suceed
My code: http://maruska.dyndns.org/comp/activity/gauche/fs/xfs.scm