Plain English
Data availability is the guarantee that all the transaction data a rollup needs is published somewhere anyone can access. Without DA, a rollup could publish a state root without showing the underlying transactions — and users could not reconstruct or challenge the chain. DA is the bottleneck for rollup costs.
How it actually works
Ethereum L1 was historically the only DA layer; EIP-4844 (proto-danksharding) introduced “blobs” — cheap temporary data storage that cut L2 fees by ~10x in early 2024. Celestia, EigenDA, and Avail are specialized DA-only chains that L2s can use instead of Ethereum for even cheaper data. Each has its own security and pricing trade-offs.
What it means for you
DA choice is one of the biggest L2 architecture decisions. Rollups using Ethereum DA inherit full Ethereum security but pay more. Rollups using third-party DA (sometimes called “validiums” or “rollups with external DA”) are cheaper but inherit weaker security from the DA layer. Read your favorite L2’s DA configuration before treating its “Ethereum security” claims at face value.
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Educational content only. Not investment, tax, or legal advice.