Discussion on the Importance of Data Availability for Layer 2

There has always been controversy regarding the data availability of Layer 2 in the Ethereum ecosystem. Some researchers believe that not using Ethereum for data availability cannot be considered L2. If this perspective is followed, many existing scaling solutions will lose their L2 qualification, including some well-known projects.

So, what exactly is data availability? What data availability challenges does Layer 2 face? Why does the data availability layer provoke so much controversy in Layer 2? This article will focus on these questions, attempting to unveil the mystery of data availability.

Definition of Data Availability

In short, data availability refers to the ability of block producers to publish all transaction data of a block to the network, enabling validators to download it. If block producers release complete data and allow validators to download it, we say the data is available; if concealing part of the data results in validators being unable to download the complete data, then the data is unavailable.

The difference between data availability and retrievability

The concepts of data availability and data retrievability are often confused, but there is actually a significant difference between them:

• Data availability refers to the stage after block production when it has not yet been added to the blockchain through consensus. It relates to whether newly released data can be agreed upon through consensus, rather than historical data.

• Data retrievability involves the stage after data has been consensus and permanently stored on the blockchain, which is the ability to retrieve historical data. In Ethereum, nodes that store all historical data are called archive nodes.

There is a view that the term "data availability" may cause misunderstanding, and it is suggested to change it to "data release" for greater accuracy.

Data Availability Issues in Layer 2

Although the concept of data availability originated from Ethereum, we are currently more focused on data availability at the Layer 2 level.

In Layer 2, the sequencer ###, as the block producer, needs to publish sufficient transaction data for validators to check the validity of transactions. This process faces two main issues:

1. Ensure the verification mechanism is secure.
2. Reduce the cost of data release

( Verification Mechanism Security

Different types of Layer 2 use different validation methods:

• Optimistic Rollup uses fraud proofs. If the sequencer does not publish complete data, challengers will be unable to initiate valid challenges.

• Although ZK Rollup does not require data availability for validity proofs, it still needs it overall. Without retrievable block data, users will not know their balances and may lose assets.

To ensure verification security, current L2 sequencers typically publish both state data and transaction data on the more secure Ethereum, relying on Ethereum for settlement and obtaining data availability.

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) Reduce publishing costs

Currently, Layer 2 places data availability and settlement on Ethereum. Although the security is high, the costs are enormous. The Gas fees that users pay to Layer 2 are mainly composed of two parts: the Gas for executing transactions on Layer 2 and the Gas for submitting data to Layer 1. The latter accounts for a large portion, with the transaction data ensuring data availability being the major part.

There are mainly two ways to reduce costs:

• Reduce the cost of publishing data on L1, such as the upcoming EIP-4844 upgrade.

• Decouple data availability from L1, without using Ethereum as the data availability layer.

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Controversy over Layer 2 Data Availability Layer

The rise of modular blockchains has opened up new possibilities for Layer 2. Modular blockchains decouple the core functionalities of blockchains, forming relatively independent components, and enhance performance by combining dedicated networks.

Currently, modular blockchains are generally divided into four layers: execution layer, settlement layer, consensus layer, and data availability layer. Existing L2s separate the execution layer from Ethereum, but the functions of the other three layers are still performed on Ethereum. However, due to cost considerations, many L2s are preparing to also separate the data availability layer from Ethereum.

However, the Ethereum community seems to be unwilling to allow L2 to obtain data availability from elsewhere. There is a viewpoint that if Ethereum is not used as the data availability layer, it does not count as a Rollup, and therefore is not an L2. The latest definition from L2BEAT also points out that scaling solutions that do not publish data on L1 do not belong to L2, because off-chain data availability solutions cannot guarantee that operators will provide the published data.

![Why is data availability so important for Layer 2?])https://img-cdn.gateio.im/webp-social/moments-f2df16558e09d770ac31a2a44ea27773.webp###

This persistence may stem from security concerns, but it could also reflect worries about the destabilization of Ethereum's status. If L2 also strips away the data availability layer, it essentially undermines the reliance on Ethereum's security, which could pose a threat to Ethereum's status.

Regardless, projects related to data availability layers are still thriving. In the future, we will see more innovative data availability solutions and projects emerging, bringing new possibilities for blockchain scalability.