Library · Crypto, word by word · Infrastructure and development
What is data availability?
Data availability is the guarantee that the full data behind a block or rollup batch has actually been published, so anyone can download it and check it. If the data is withheld, nobody can verify the transactions or rebuild balances, even if a summary or proof was posted.
What it means for you
On a rollup, data availability decides whether you can get out on your own. If the transaction data is posted to the main chain, anyone can reconstruct balances and help you withdraw if the operator disappears; if the data sits with a small committee off chain, withholding it can freeze withdrawals. Check where a layer 2 posts its data before you deposit.
How it works
Rollups compress many transactions into batches and post the data so independent verifiers can confirm the proposed state matches the actual transactions. Since EIP-4844, rollups can post this data in blobs of 4,096 field elements of 32 bytes (128 KB each), which nodes keep for 4,096 epochs, about 18 days, before pruning. Data availability sampling lets nodes check availability without downloading everything: data is erasure-coded so that if any original piece is missing, half the expanded data is missing, and each node downloads a few random pieces to detect that.
Sources: ethereum.org: Data availability, EIP-4844: Shard Blob Transactions · checked 4 October 2026
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