Data Layer

The data layer, often called the data availability layer, is where a blockchain publishes the raw transaction data that anyone needs to independently verify the chain's state. If a rollup posts only a summary of its results, users cannot rebuild balances or challenge a bad state unless the underlying data is genuinely published and retrievable — that is this layer's job. Ethereum performs the role for its rollups through blob storage, and dedicated data availability networks offer it as a standalone service. Cheap data is a major cost driver: rollup fees fall largely because publishing data got cheaper. The risk to understand is data withholding — if the data is not available, exits and fraud proofs can stall even while the chain looks healthy.