# Comprehensive Review of Storage Optimization Techniques in Blockchain Systems
## 4 Methods
### Ipfs  
The Interplanetary File System (IPFS) [68] is a distributed file storage, sharing, and persistence protocol. Unlike traditional systems that rely on location-based server IP addressing, IPFS uses content-based addressing. This is achieved by assigning a unique cryptographic hash to each stored file, enabling efficient identification and retrieval. When a file is uploaded to IPFS, it is assigned a hash known as the content identifier (CID). For instance, as shown in Figure 6, if a blockchain-stored file (TX) of 500 bytes is uploaded to IPFS, it returns a hash of 46 bytes. Once uploaded, the file is stored on multiple nodes within the network, which distribute it through a peer-to-peer (P2P) network. Users can access the file using its unique CID, regardless of which node is storing it. This content-addressing system enables faster, more secure, and efficient sharing of internet resources. In the context of blockchain, transaction data can often be substantial, reaching tens of kilobytes, with individual transactions typically being at least 200 bytes in size. In contrast, the IPFS hash representing a file is typically only a few dozen bytes. By transferring certain blockchain data to IPFS and storing the resulting IPFS hash within the blockchain block, significant reductions in storage space requirements can be achieved [69]. This integration of IPFS with blockchain not only optimizes storage efficiency but also enhances the scalability of blockchain networks. Currently, many scholars, both domestically and internationally, are leveraging IPFS as an off-chain storage solution and proposing various optimization strategies for expanding blockchain storage capacity. To address the storage bottlenecks in high-capacity data storage on the blockchain, particularly in managing large files and enabling automated storage management, [PERSON] et al. [70] proposed a distributed architecture using blockchain and IPFS. The decentralized storage protocol of IPFS allows large files to be divided into multiple data shards, which are then distributed across various nodes. Each shard generates a unique cryptographic hash, with the content securely stored on IPFS. In this architecture, the blockchain structure becomes optimized; each time a file is uploaded to IPFS, an automatically generated cryptographic hash is recorded on the blockchain, serving as the unique identifier for that file. In this solution, smart contracts play a crucial role in managing interactions between blockchain and IPFS. The smart contracts automatically log the cryptographic hash of the uploaded file and enforce access controls when users request access. Upon uploading a file to IPFS, the smart contract generates the file hash and stores it on the blockchain, along with metadata such as the file name, upload timestamp, and file owner. This ensures that \begin{table}
\begin{tabular}{c c c c} \hline \hline
**References** & **Main Technologies** & **Pruning Strategies** & **Usage Scenario** \\ \hline [PERSON] [1] & Merkle tree & Time-based & Public blockchain \\ [PERSON] [64] & RSA accumulator,snapshot & Historical data-based & Public blockchain \\ [PERSON] [65] & MOF-BC & IOT data-based & Public and private blockchains \\ [PERSON] [66] & SPV,FPLE & invalid data-based & Public blockchain \\ [PERSON] [67] & PSO algorithm & access frequency-based & Public blockchain \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Pruning techniques for reducing storage redundancy. Figure 6: IPFS network architecture. only authorized users can access these files, effectively managing data access through a permission management mechanism. When a user requests file access, the smart contract verifies their identity to confirm the appropriate permissions, then locates the file using the cryptographic hash stored on the blockchain, enhancing both data security and privacy. By combining IPFS with smart contracts, this approach not only reduces redundancy in large file storage but also facilitates automated data management. [PERSON] et al.