# SASLedger: A Secured, Accelerated Scalable Storage Solution for Distributed Ledger Systems
###### Abstract  
Blockchain technology provides a \"tamper-proof distributed ledger\" for its users. Typically, to ensure the integrity and immutability of the transaction data, each node in a blockchain network retains a full copy of the ledger; however, this characteristic imposes an increasing storage burden upon each node with the accumulation of data. In this paper, an off-chain solution is introduced to relieve the storage burden of blockchain nodes while ensuring the integrity of the off-chain data. In our solution, an off-chain remote DB server stores the fully replicated data while the nodes only store the commitments of the data to verify whether the off-chain data are tampered with. To minimize the influence on performance, the nodes will store data locally at first and transfer it to the remote DB server when otherwise idle. Our solution also supports accessing all historical data for newly joined nodes through a snapshot mechanism. The solution is implemented based on the Hyperledger Fabric (HLF). Experiments show that our solution reduces the block data for blockchain nodes by 93.3% compared to the original HLF and that our advanced solution enhances the TPS by 9.6% compared to our primary solution. blockchain; scalability; storage; data integrity; performance +
Footnote †: journal:  
Bitcoin node has reached 366.51 GB [6] and the data size of a Ethereum node has reached 987.54 GB [7] by 28 September 2021; for permissioned blockchains, the issue has also caused concern [8; 9]. The storage burden is becoming more onerous for individual participants who run blockchain nodes with their personal computers. This situation may injure the decentralized character of blockchain systems since only wealthy individuals or organizations can afford the increasing storage scaling demand. Methods proposed to solve the storage scalability issue of blockchain systems are divided into \"on-chain\" solutions and \"off-chain\" solutions. On-chain solutions reduce the contents stored in each node by altering the range of consensus or the contents of transactions [10; 11; 12; 13]. Off-chain solutions provide off-chain storage devices to store data, but most of them focus on reducing the data size before the data are uploaded to blockchains [14; 15; 16; 17]. This approach uses blockchain as a proof repository to ensure the integrity of off-chain data, but the off-chain data cannot be retrieved through blockchain node, on the contrary, block archiver [18] reduces the data size of the data that has been uploaded to the blockchain and stored in the blockchain nodes, but block archiver fails to ensure the integrity of the data stored off-chain, which severely damages the tamper-proof property of the original blockchain system. To bridge this gap, an off-chain solution for the data that has been uploaded to the blockchain with tamper-proof property is proposed in this paper. The data are eliminated from the blockchain node and transmitted to a remote DB server while the node saves a concise vector commitment (VC) [19] to ensure the integrity of the data stored off-chain. The contributions made by the present research are as follows:  
1. An off-chain solution to solve the data scalability issue of blockchain systems while ensuring the integrity of the data stored off-chain is proposed, the target of this solution is to reduce the size of the data that has been uploaded to the blockchain and stored in the blockchain nodes. Each node saves a concise VC to ensure the integrity of the data of a block while the raw data are eliminated from the node. 2. The performance of our solution is improved compared to our primary solution \"xFabLEDger\" [20] by separating the transaction-processing phase and the data-reduction phase. The data reduction is performed when a blockchain node is backed up to avoid read-write conflicts and negative impact on performance. 3. The solution is implemented based on Hyperledger Fabric (HLF) V2.3.2 [21], and storage experiments and performance experiments are conducted to prove the effectiveness of our solution.