http://blog.chinaunix.net/space.php?uid=20740092&do=blog&cuid=1108291
sudo apt-get install dmsetup cryptsetup
time sudo dd if=/dev/zero of=svn.img bs=1M count=35000
sudo losetup /dev/loop6 svn.img
sudo cryptsetup -y create svndisk /dev/loop6
sudo mkfs.ext4 /dev/mapper/svndisk
sudo mkdir svndisk
sudo mount /dev/mapper/svndisk svndisk
sudo chown karlzheng.karlzheng svndisk/ -R
sudo umount svndisk
sudo cryptsetup remove /dev/mapper/svndisk
sudo losetup -d /dev/loop6