from: http://user-mode-linux.sourceforge.net/resize.html 

#> e2fsck -f data3_fs.ext3
#> dd if=/dev/zero of=data3_fs.ext3 bs=1 count=1 seek=6G conv=notrunc
#> resize2fs -p data3_fs.ext3

shrink: ext2resize 

#> /sbin/tune2fs -O ^has_journal /dev/hdb1
#> umount /dev/hdbX


10M = 10240 blocks.
6G = 1572864 blocks.