Mainstream disaster recovery protection solutions are usually designed across multiple infrastructure layers. The host layer is included because application servers, operating systems, clusters, and host multipathing must support failover and service recovery. The network layer is included because production and DR sites require reliable inter-site connectivity, routing, bandwidth, latency control, and network failover design. The storage layer is also a core DR layer because data replication, consistency groups, snapshots, and storage failover are implemented at the storage system level. Application-layer protection can exist in some specialized application-aware DR designs, but in the mainstream Huawei storage DR protection model, the commonly emphasized layers are host, network, and storage. Therefore, the correct choices are host layer, network layer, and storage layer.