## 3 System Model
### RSU Cluster Cooperative Storage System Model  
In blockchain-enabled social Internet of Vehicles, RSU nodes collect reputation change information generated by vehicles within their service range. This information is encapsulated into blocks as transactions and submitted to the blockchain network through a consensus mechanism for recording. As full nodes in the blockchain network, RSUs are required to store a complete copy of the blockchain data locally to provide services to vehicles. However, as the blockchain network grows over time, the increasing length and volume of blockchain data exceed the storage capacity of individual RSUs, preventing resource-limited RSUs from participating in the blockchain consensus process as full nodes. To address this issue, the model proposed in this paper organizes multiple RSUs into collaborative storage clusters, enabling them to jointly maintain blockchain data integrity. Within each cluster, RSUs store only a portion of the blockchain data while still providing essential services such as reputation queries and transaction verification for vehicles. If an RSU lacks the required block data locally, it can retrieve the missing blocks from other RSUs within the cluster, ensuring service continuity and efficiency. As shown in Figure 1, the system primarily consists of vehicles, RSUs, a cloud server, and a blockchain network that provides reputation activity recording and authentication for the vehicular social network. Vehicles act as primary users, collecting information about themselves and their surroundings while interacting and communicating with other vehicles or RSUs through built-in communication devices. When multiple vehicles generate activities within the social network, all reputation update information related to the involved vehicles is encapsulated into blocks by RSUs and appended to the blockchain via the consensus network connected to the cloud server. The vehicular network cluster is defined as the set of multiple RSUs and vehicles within a specific region. The set of vehicles participating in social activities is represented as \(V=\{v_{1},v_{2},\cdots,v_{M}\}\), the set of RSUs that construct the blockchain network, store blockchain data, and provide services is denoted as \(R=\{r_{1},r_{2},\cdots,r_{N}\}\), where the available storage capacity of an RSU \(r_{i}\) is represented as \(rc_{i}\). Assuming that the current blockchain state consists of K blocks, the complete blockchain ledger is expressed as \(B=\{b_{1},b_{2},\cdots,b_{K}\}\), where the size of block \(b_{k}\) is defined as \(s_{k}\). In the cooperative storage system of the RSU cluster, the RSU cluster is represented as \(CLU=\{C_{1},C_{2},\cdots,C_{L}\}\), where each cluster \(C_{l}=\{r_{1}^{l},r_{2}^{l},\cdots,r_{N_{l}}^{l}\}\) consists of multiple RSUs that collectively store all blocks in the blockchain \(B\), and \(N_{l}\) is the number of RSU nodes in cluster \(C_{l}\). In the system, RSU nodes and cloud nodes act as consensus nodes to construct the blockchain network collaboratively, maintaining consistency and integrity while providing query and verification services to vehicle users. When vehicle users need to obtain data from the blockchain, such as vehicle reputation status and historical reputation change records, they can choose to retrieve this information either from nearby RSU nodes or remote cloud nodes based on their current location. Upon receiving a query request from a vehicle, the RSU or cloud node queries the local or cluster ledger for block data and transmits the complete block information to the vehicle. Meanwhile, all vehicles participating in the SloV within the cluster store lightweight block header data. Upon retrieving block data from RSU nodes or the cloud nodes, they can independently verify the integrity and authenticity of the data using the locally stored block headers, ensuring data reliability.