This application describes a system startup method and apparatus. The method may include establishing a mapping relationship between address space of a first storage device and address space of a second storage device. The method may also include receiving a read/write request sent to the first storage device. Furthermore, the method may include when the read/write request is a write request for the first storage device, writing data to a second address in the second storage device based on a first address in the first storage device in the write request and the mapping relationship. Or, when the read/write request is a read request for the first storage device, determining whether data has been written to a fourth address corresponding to a third address in the read request. The method may further include reading data from the fourth address when the data has been written to the fourth address, or reading data from the third address when no data has been written to the fourth address.