I don't think you can just do a cold re-write of that size without domain knowledge. I would first try to refactor the existing system just to reduce the code s

I don't think you can just do a cold re-write of that size without domain knowledge. I would first try to refactor the existing system just to reduce the code size. That big a system probably has horrific code and you can easily shrink it quickly. Just finding duplicate code will have an impact. Pulling out to open source systems like file utilities based code. Basically I would first try to reduce the size of the problem while trying to get domain expertise. I wouldn't consider a rewrite at this stage...