Cold data storage is more and more important in Cloud computing and big data infrastructure. Like Amazon Website Service, Facebook, Alibaba, many cloud and internet service providers invest more and more on high durability, low cost cold data storage system. In open source world, there is a few project is specifically built for cold data storage. This talk explains how an open source distributed storage project -- sheepdog is used as a cold data storage engine. It is not only about source code, people will aware of special requirement and challenge of cold data storage, which is apparently different from online data storage system. I hope this talk may enlighten people design and implement product quality cold data storage engine for their own usage.