What is a Blob?
A blob (Binary Large Object) is a new type of data storage on Ethereum, introduced by EIP-4844 (also called Proto-Danksharding). Blobs provide a much cheaper way for Layer 2 rollups to post their transaction data to Ethereum, dramatically reducing L2 fees.
Before blobs, rollups posted all transaction data as calldata, which is expensive because every node must process and store it permanently. Blobs are cheaper because they’re stored separately from the execution layer and have a limited retention period (~18 days).
Why Blobs Were Needed
Layer 2 rollups (Arbitrum, Optimism, Base) batch transactions off-chain and post the compressed data to Ethereum for security. This data posting was the largest cost component of L2 fees.
| Before EIP-4844 | After EIP-4844 |
|---|---|
| Rollups post data as calldata | Rollups post data as blobs |
| Every node processes all data | Only blobs are stored separately |
| Data stored permanently | Data pruned after ~18 days |
| L2 fees: $0.50-2.00 | L2 fees: $0.01-0.10 |
How Blobs Work
- Rollup posts a blob containing compressed batch data to Ethereum
- The blob is referenced in the block but not executed by the EVM
- A proof (KZG commitment) ensures the data is available and correct
- Data availability nodes store the blob data (not all nodes)
- After ~18 days, blob data is pruned (the proof remains, but raw data is removed)
The 18-day retention period is sufficient because rollups need the data for challenge/fraud-proof windows (typically 7 days).
Impact on L2 Costs
EIP-4844 (implemented in March 2024) caused a dramatic drop in L2 transaction fees:
- Arbitrum: Average fees dropped from ~$0.50 to ~$0.05
- Optimism: Average fees dropped from ~$0.40 to ~$0.03
- Base: Average fees dropped from ~$0.30 to ~$0.02
This made L2 transactions viable for micro-transactions, gaming, and high-frequency DeFi.
The Path to Full Danksharding
EIP-4844 is “Proto-Danksharding” — the first step. Full Danksharding will further increase blob capacity:
- EIP-4844: ~3 blobs per block (current)
- Full Danksharding: 64+ blobs per block (future)
- Impact: 10-100x more L2 capacity, further reducing fees
Frequently Asked Questions
Q: What happens to L2 data after blobs are pruned? A: The raw blob data is removed after ~18 days, but the cryptographic commitment (proof) remains permanently. Rollups can reconstruct the data from their own nodes or from third-party data availability providers. The fraud-proof window (7 days) is much shorter than the blob retention period.
Q: Do blobs increase Ethereum’s throughput? A: Not directly for Ethereum L1. But they dramatically increase effective throughput of the Ethereum ecosystem by making L2s cheaper and more accessible. The total system (L1 + L2s) processes far more transactions.
Q: How do blobs affect ETH economics? A: Blobs have their own fee market (separate from regular gas). Blob fees are burned, similar to EIP-1559’s base fee. During high L2 activity, blob fees contribute to ETH burning.