CashboardGlossary · Onchain
What is data availability?
Data availability means the data behind a chain's blocks is published where anyone can download it, so they can check the chain and rebuild its state.
How does data availability work?
A rollup does its work away from Ethereum and then asks everyone to accept the result. That only holds up if the raw transaction data is public. With it, anyone can recompute balances, watchers on an optimistic rollup can prove fraud, and you can leave without the operator's help. Without it, a posted state is a claim nobody can check.
Where the data goes is the line L2BEAT draws between kinds of chains. A rollup puts it on Ethereum, in calldata at first and, since the Dencun upgrade on March 13, 2024, mostly in blobs. Nodes only have to keep blobs for about 18 days, long enough for anyone who needs the data to fetch it. A chain that posts its data somewhere else, to a committee or a network such as Celestia or EigenDA, is an optimium if it runs fraud proofs and a validium if it runs validity proofs. Cheaper data, one more party to trust.
Ethereum keeps widening its own lane. PeerDAS went live with Fusaka on December 3, 2025 and lets nodes confirm blob data is out there by sampling pieces of it instead of downloading every blob. Two follow-up forks then raised the target from 6 blobs a block to 10 in December and to 14 on January 7, 2026, with room for 21.
Say a made-up optimium's data committee goes dark while the chain keeps producing blocks. Balances still update, but nobody outside can see the transactions behind them, so a bad state could not be challenged and a user could not prove what they own in order to leave. That is the risk the cheaper data buys.
Also called: DA, DA layer, data availability layer.
Where does data availability show up in Cashboard?
The Ethereum pulse prices Ethereum's own data lane: the blob base fee, what one 128 KiB blob costs in dollars and how full blob space ran over the last 20 blocks against the per-block maximum. The L2 scoreboard carries growthepie's label for each chain, such as Optimistic Rollup, ZK Rollup or Optimium, in the hover text of its L2BEAT stage tag, or under the name where L2BEAT gives no stage. Neither widget names the DA layer a chain uses. L2BEAT's page for the chain does.
Frequently asked questions
What is the difference between a rollup and a validium?
Where the data lives. A rollup publishes its transaction data on Ethereum, so anyone can rebuild its state from there. A validium posts validity proofs to Ethereum but keeps the data elsewhere, so you also trust whoever holds it. An optimium makes the same trade with fraud proofs.
Does data availability change what I pay on an L2?
Yes. Part of every OP Mainnet fee is the L1 data fee, the cost of publishing your transaction's data to Ethereum. When blobs arrived on March 13, 2024, Base's Jesse Pollak shared a before and after for one Base transaction: $0.31, then about $0.0005. Chains that post data to a cheaper outside layer can pay less still, and ask you to trust that layer.
Related terms
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