Discussion on the Importance of Data Availability for Layer 2

Data availability is a key concept in blockchain technology, particularly important for Layer2(L2) solutions. This article will delve into the meaning of data availability, the challenges that L2 faces regarding data availability, and the controversies surrounding the L2 data availability layer.

Definition of Data Availability

Data availability refers to the ability of block producers to publish all transaction data from a block to the network, allowing validators to download and verify it. When block producers publish complete data and allow validators to download it, we consider the data to be available; conversely, if concealing part of the data prevents validators from obtaining complete information, the data is considered unavailable.

It is important to note that data availability and data retrievability are two different concepts:

• Data availability focuses on the stage after a new block is produced but before it is added to the blockchain through consensus.
• Data retrievability refers to historical data that has been consensus-validated and permanently stored on the blockchain.

Some believe that the term "data availability" may be misleading and suggest changing it to "data release" for a more accurate description of its function.

Challenges of Data Availability in L2

In L2, the sequencer ( Sequencer ) plays the role of a block producer and needs to publish enough transaction data for verification. L2 faces two main challenges: ensuring the security of the verification mechanism and reducing the cost of data publication.

Verification mechanism security

Different types of L2 use different verification methods:

• Optimistic Rollup uses fraud proofs: If the sequencer does not publish complete data, challengers will not be able to initiate a valid challenge.
• ZK Rollup uses validity proofs: Although the proof itself does not rely on data availability, users still need complete data to verify their asset status.

To ensure verification security, most L2s currently choose to publish state data and transaction data on Ethereum, leveraging its security and data availability.

Reduce data publishing costs

The Gas fees paid by L2 users mainly consist of two parts: Gas for executing transactions on L2 and Gas for submitting data to L1. Among these, the latter takes up the majority, and the transaction data that ensures data availability constitutes a significant portion of that.

There are mainly two ways to reduce costs:

1. Reduce the cost of publishing data on L1, such as the upcoming EIP-4844 upgrade.
2. Separate the data availability layer from L1, similar to how Rollups detach transaction execution from L1.

L2 Data Availability Layer Controversy

The concept of modular blockchains provides a background for understanding the controversies surrounding L2 data availability layers. Modular blockchains divide blockchain functions into four parts: execution layer, settlement layer, consensus layer, and data availability layer.

Currently, L2 has separated the execution layer from Ethereum, but the other three layers still rely on Ethereum. However, for cost considerations, many L2s are considering peeling the data availability layer off from Ethereum as well.

This trend has sparked controversy. Some members of the Ethereum community believe that solutions that do not use Ethereum as a data availability layer should not be considered L2. They are concerned that if L2 separates the data availability layer from Ethereum, it may weaken the reliance on Ethereum's security, thereby threatening Ethereum's position.

Despite the controversies, innovation and project development around the data availability layer are still thriving. In the future, we may see more solutions and projects emerging in this field.