A decentralized data availability (DA) layer is a system that stores and provides consensus on the availability of blockchain data. It is the location where transaction data is stored, and its role is critical for blockchains to achieve data availability, which is the idea that all transaction-related data is available to nodes on the blockchain network, allowing nodes to independently verify transactions and compute the blockchain’s state without the need to trust one another. The challenges presented by needing data availability are requiring nodes to download and verify data, which reduces throughput, and using on-chain storage for an increasingly large amount of information, which limits the number of entities who can run node infrastructure. To address this, modular chains are often designed to scale throughput by separating data availability from consensus and execution, and Ethereum's current scaling roadmap includes plans to implement data sharding, where various clusters of nodes store distinct pieces of data, enabling multiple data availability layers.