# Research on Blockchain Data Availability and Storage Scalability
## 1 Introduction  
Blockchain is a distributed database that relies on P2P (Peer-to-Peer) networks and has the characteristics of being decentralized, secure, reliable, and traceable [1]. To ensure its characteristics, blockchain adopts a highly redundant data storage method wherein each node stores all blocks as a Full Node. The characteristics of blocks that can only be added and cannot be deleted make the total number of blocks accumulate over time, and nodes face increasingly severe storage pressure. Resource-constrained nodes have to choose to either become degraded nodes or exit the system, leading to a decrease in data availability and causing the problem of storage scalability in blockchain. Full nodes store complete block data and have full verification functions. Degraded nodes store partial block data and have partial verification functions.  
Currently, solving the problem of storage scalability is carried out on two levels: (1) proposing scalable storage schemes based on experience, such as data sharding, data reduction, and multi-node-type collaborative storage [2], and (2) building a scalable storage model to guide the development of scalable storage solution schemes [1]. The Scalable Model for Blockchain Storage System (SMSBS) utilizes the transaction verification characteristics of UTXO (Unspent Transaction Outputs) and account type data, storing only some key data and storing it in the form of data sharding and thereby reducing data redundancy while giving nodes full functionality. However, none of the previous relevant studies have provided guarantees of data availability.  
One important reason for the problem of blockchain storage scalability is the contradiction between data redundancy and data availability. On the one hand, blockchain utilizes P2P networks to achieve node communication and data sharing. To ensure highdata availability, nodes need to store as much block data as possible, resulting in high data redundancy and poor storage scalability. On the other hand, lower data redundancy can improve storage scalability, but it will reduce data availability and ultimately affect the normal operation of blockchain.  
According to the above analysis, when improving the scalability of blockchain storage while also considering data availability, it is necessary to establish a relationship model linking data redundancy and data availability. So far, no measurement model for blockchain data availability has been found in the collected literature. Therefore, this article first proposes a data availability definition for blockchain based on the existing definition of data availability in P2P networks. Then, by analyzing the data synchronization process and the transaction lifecycle, a Data Availability Measurement Model for Blockchain (DAMMB) is constructed, and the data availability levels of different storage schemes are measured. Finally, a model of the relationship between data availability and storage scalability is constructed to guide the setting of data redundancy in scalable storage schemes. The contributions of this article are as follows:  
1. It proposes a definition of data availability for blockchain;
2. It summarizes the key factors that affect data availability during the data synchronization process and the transaction lifecycle;
3. Based on the key factors affecting data availability, combined with information on node types, it proposes a Data Availability Measurement Model for Blockchain (DAMMB).
4. It builds a model of the relationship between data availability and storage scalability to find the range of data redundancy that meets the target data availability.