Crypto Gloss

Blob Space (EIP-4844)

Blob space is a new data storage lane on Ethereum introduced by EIP-4844, providing rollups with a cheap, dedicated channel for posting transaction data. Prior to EIP-4844, rollups posted data as expensive CALLDATA to Ethereum transactions. Blobs are larger, cheaper, and automatically pruned after ~18 days — making them ideal for rollup data that needs short-term availability.

The Problem Before Blobs

Layer 2 rollups scale Ethereum by:

  1. Executing transactions off-chain
  2. Posting compressed transaction data to Ethereum (for verification and reconstruction)
  3. Submitting a validity proof or fraud proof to confirm execution

Step 2 was the bottleneck: posting data as Ethereum CALLDATA was expensive and competed with regular transactions for block space. Even with massive compression, L2 fees during Ethereum congestion could spike.

How Blobs Work

EIP-4844 added a new transaction type: blob-carrying transactions:

  • Each block can carry 3–6 blobs (target: 3)
  • Each blob is ~128 KB of raw data
  • Blob data is committed to using KZG polynomial commitments — a cryptographic proof that the data exists
  • Blobs are pruned from full nodes after ~18 days; only the KZG commitment is kept permanently on-chain
  • Blob gas market: Separate fee market from regular Ethereum gas — blobs have their own base fee that adjusts based on blob demand

Impact on L2 Costs

Period L2 Data Cost
Pre-Dencun ~10–50 gwei per byte in CALLDATA
Post-Dencun ~1/100th of previous cost in blob space

After Dencun, L2 transaction fees dropped 80–95% on most rollups. Arbitrum, Optimism, Base, and zkSync all reported dramatic cost reductions.

Full Danksharding Vision

EIP-4844 is “Proto-Danksharding” — a partial implementation. Full Danksharding (future upgrade) will:

  • Increase blob count from 3–6 to 64+ per block
  • Add Data Availability Sampling (DAS) so light clients can verify blobs
  • Enable massive further scaling for the rollup ecosystem

Sources

  • EIP-4844 specification: eips.ethereum.org/EIPS/eip-4844
  • Tim Beiko’s Dencun summary
  • L2 fee impact analysis: l2fees.info