// GLOSSARY -- WEB3 INFRASTRUCTURE

What is Data Availability?

1 min read Updated

Data availability (DA) is the guarantee that all data needed to verify blockchain state transitions has been published and is accessible — a critical property for rollup security and blockchain scalability.

WHY IT MATTERS

For rollups to be secure, the transaction data they produce must be available for anyone to verify. If a rollup posts a state root but withholds the underlying data, no one can prove fraud (optimistic) or verify correctness independently.

Data availability solutions include: posting to Ethereum calldata (expensive but secure), Ethereum blobs via EIP-4844 (cheaper, designed for DA), and dedicated DA layers (Celestia, EigenDA, Avail).

The DA landscape is a key scalability bottleneck — cheaper DA means cheaper rollup transactions. EIP-4844 reduced L2 costs dramatically, and dedicated DA layers promise further reductions.

FREQUENTLY ASKED QUESTIONS

Why does data availability matter?
Without available data, rollup users can't verify state, construct fraud proofs, or exit the rollup independently. DA is what makes rollups trustless rather than dependent on the sequencer.
What is EIP-4844?
Also called 'Proto-Danksharding,' it introduced blob transactions — a cheaper way for rollups to post data to Ethereum. It reduced L2 transaction costs by 10-100x when implemented in early 2024.
What is Celestia?
A dedicated DA layer — a blockchain optimized solely for data availability. Rollups can post data to Celestia instead of Ethereum, trading some security for significantly lower costs.

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