In a backup method, a first controller of a storage system receives a file process request, and divides the file process request into a plurality of file operations. The first controller processes each of the file operations to generate multiple pieces of file operation information. And then, the first controller writes all of the multiple pieces of file operation information into a cache protected area. When the first controller fails, it stores the multiple pieces of file operation information to a disk protected area of a disk in the storage system. After the first controller is powered on again, the first controller copies the multiple pieces of file operation information from the disk protected area to the cache protected area. And then, it writes the file operation information into a write cache. At last, the first controller stores the file operation information into a disk of the storage system.