Why Rollups Need Data Availability Layers

For years, Ethereum’s scalability trilemma—balancing decentralization, security, and throughput—has dominated discussions. The community’s solution? A rollup-centric approach. But here’s the catch: most rollups rely heavily on Ethereum as a data availability (DA) layer. Without DA, rollups lose their guarantees of execution integrity and user recoverability.

The Problem with Calldata

Currently, rollups use Ethereum’s calldata for DA, but it’s expensive—consuming ~80% of a rollup operator’s gas fees. Enter EIP-4844, aka Proto-Danksharding. This upgrade introduces blob-carrying transactions, a new format designed explicitly for DA. Unlike calldata, blobs are cheaper because they’re not executable by smart contracts—they’re purely for storage.

How Blobs Work

• Temporary Storage: Blobs persist for ~18 days (4096 epochs), long enough for validators to verify data.
• Separate Fee Market: Blob gas prices operate independently from execution gas, shielding rollups from L1 congestion spikes.
• KZG Commitments: Each blob includes a cryptographic commitment for efficient verification without full data exposure.

Scroll’s Adaptation to EIP-4844

As a zkRollup, Scroll traditionally committed batch transactions via calldata. Post-EIP-4844, it shifts to blobs, reducing costs while maintaining security. The PI circuit—a critical component in Scroll’s proof system—now validates blob consistency using polynomial evaluations across elliptic curves (BLS12-381 vs. BN254). A proof-of-concept achieves this with ~28M circuit constraints, taking 139 seconds per proof on an M1 MacBook Pro.

What’s Next? Danksharding

Proto-Danksharding is just the beginning. The full Danksharding upgrade will introduce data availability sampling (DAS), enabling nodes to verify large datasets without downloading entire blocks. Think of it as crowd-sourced DA validation—a game-changer for scalability.

Final Thought: While EIP-4844 is a leap forward, its current blob capacity (~100 TPS across all rollups) remains limited. Until Danksharding arrives, rollups must balance cost-efficiency with additional trust assumptions.