Data Availability: Challenges and Controversies Facing L2

Data availability refers to the ability of block producers to publish all transaction data of a block to the network for validators to download. This concept originated in Ethereum, but currently, more attention is focused on data availability issues at the L2 level.

In L2, the sorter, as a block producer, needs to publish sufficient transaction data for validators to check the validity of the transactions. This process faces two major challenges: ensuring the security of the verification mechanism and reducing the cost of data publication.

For OP Rollup, if the sequencer does not publish complete data, challengers will be unable to initiate valid challenges. Although ZK Rollup's validity proof does not rely on data availability, it still requires complete data to protect user assets. To this end, L2 currently generally publishes state data and transaction data on Ethereum to achieve security and data availability.

However, this practice leads to significant costs. The Gas fees that users pay to L2 are primarily generated by L2 submitting data to L1, with transaction data publication being the main component. To reduce the overall costs of L2, it is necessary to lower the data publishing costs.

There are two main methods: one is to reduce the cost of publishing data on L1, such as the upcoming EIP-4844 upgrade; the second is to detach data availability from L1, not using Ethereum as a data availability layer.

The concept of modular blockchain provides a theoretical foundation for the second approach. It decouples blockchain functionality into execution layer, settlement layer, consensus layer, and data availability layer. Currently, L2 has separated the execution layer from Ethereum, and some L2 are considering further separating the data availability layer.

However, this trend has sparked controversy. Researchers from the Ethereum Foundation believe that not using Ethereum as a data availability layer cannot be considered L2. L2BEAT also pointed out that scaling solutions that do not publish data on L1 do not qualify as L2, as there is no guarantee that operators will provide the published data.

These views may stem from security considerations, but they may also reflect concerns about the weakening status of Ethereum. If L2 separates the data availability layer from Ethereum, it could weaken the reliance on Ethereum's security and potentially threaten Ethereum's position.

Despite the controversies, projects related to the data availability layer are still thriving. There are currently various data availability solutions and projects in the market that are worth further attention and discussion.