The Donerail Group has built a stake in Mobile Mini, Inc. (NasdaqGS:MINI) and is pushing the world’s largest provider of portable storage solutions to explore a sale, people familiar with the matter said. Donerail has asked Mobile Mini to explore strategic alternatives, including a potential sale, given the fragmented nature of the portable storage sector, the sources said, requesting anonymity because the matter is confidential. It was not clear how Mobile Mini plans to respond. Mobile Mini did not immediately respond to a request for comment. Donerail declined to comment.