A redundancy method includes that a first disaster management function (DMF) device on a first site side receives a first request including identification information of a first virtual machine (VM) and a recovery point objective (RPO), allocates a maximum allowable delay time to each node that input/output (IO) data of the first VM passes through in a redundancy process, and sends a second request to a second DMF device on a second site side. The second request includes a maximum allowable delay time of a second replication gateway function (RGF) device on the second site side, and a maximum allowable delay time of an IO writer function (IOWF) device on the second site side and requests the second site side to perform redundancy on the first VM. Hence, the RPO requirements of the tenants can be satisfied in an entire redundancy process.