The present disclosure provides a method and apparatus for writing data in an append mode, a device and a storage medium. The present disclosure relates to the field of cloud storage technology, and can be applied to a cloud platform. The method includes: acquiring to-be-written data, and writing the to-be-written data into a magnetic disk; writing first index information of the to-be-written data in a memory; storing, in response to determining that the number of pieces of second index information is greater than a first preset threshold, the second index information into storage hardware, the second index information including the first index information; and writing first identifier information corresponding to the second index information in the memory.