# Comprehensive Review of Storage Optimization Techniques in Blockchain Systems
## 4 Methods
### Data Sharding Storage
[77] propose the Wider chain, leveraging sharding by account and unlimited shards and confirming the status of the subchains to reduce storage redundancy in blockchain systems, thereby enhancing scalability and operational efficiency. In the Wider chain, sharding by account is applied by partitioning blockchain accounts and assigning each to a distinct subchain, with each subchain responsible for processing and storing transaction data for a specific subset of accounts. This approach effectively decouples transaction data from the main chain, significantly reducing the main chain's storage burden, while nodes are required only to maintain the data relevant to their assigned subchain, thereby eliminating the need to store the entire network's data and improving storage utilization. Furthermore, Wider incorporates an unlimited sharding architecture that dynamically scales storage requirements. As the number of nodes in the blockchain network increases, new shards can be added in real time, allowing transaction data to be distributed evenly across more nodes for storage and processing. This dynamic structure enables the system to adapt flexibly to the growth in both account numbers and data volume, efficiently balancing storage loads while maintaining high performance. Compared to traditional fixed sharding schemes, this unlimited sharding approach demonstrates enhanced adaptability and flexibility in handling rising data volumes and user demands. In addition, Wider's  
Figure 10: Block division. mechanism to confirm the status of the subchains contributes to further reducing main chain data volume. Under this mechanism, the main chain no longer records each transaction's detailed information but instead maintains only the aggregated state of each subchain. Using a State Transition Function (STF), multiple transactions within each subchain are consolidated into a single state update that is recorded on the main chain which significantly minimizes the data load on the main chain while preserving transparency and data integrity within the system. Despite its advantages in reducing storage redundancy, the Wider chain design also faces challenges. For instance, under conditions of high network latency, synchronization between nodes and subchain state confirmations may be affected. Additionally, nodes must have adequate bandwidth and computational resources to handle transaction verification, especially when synchronizing across multiple subchains. Overall, these design features enhance the scalability and efficiency of blockchain systems, reduce data storage redundancy, and provide a robust theoretical and technical foundation for large-scale blockchain applications. [PERSON] et al. [78] proposed that sharded storage is a key strategy for reducing blockchain storage redundancy, effectively improving the storage and processing efficiency of resource-constrained nodes. By partitioning the blockchain ledger into multiple shards and distributing them across different nodes, the need for all nodes to store a complete ledger is eliminated, which is particularly suitable for Internet of Things (IoT) scenarios where nodes have limited storage and computational resources. Specifically, the paper presents a sharded storage method based on a Directed Acyclic Graph (DAG) structure. The DAG structure enables nodes to process events in a parallel and non-linear manner, overcoming the limitations of traditional blockchain's sequential block processing. Each node is required only to store and validate data associated with its specific shard rather than maintaining the entire blockchain ledger. This not only alleviates storage pressure but also mitigates the bottleneck of sequential processing inherent in traditional blockchains through parallel processing, significantly enhancing system throughput and overall performance.