Also, log files are written sequentially and will overwrite themselves only when the portion at the beginning of the file is no longer needed. When you shrink a log file, it will only truncate the portion at the end of that data is not needed. So you may not be able to shrink it to the target size even if much of the data is not needed, depending on where it's writing at the time. There's some good discussion of this topic on Books Online. Look up "Managing Log Files."