Discussion on the Importance of Data Availability for Layer 2

In the Ethereum ecosystem, data availability has always been a topic of great concern. Researchers have stated that without utilizing the data availability provided by Ethereum, it cannot be considered a true L2 solution. This perspective has raised questions about whether many existing projects fall under the L2 category.

So, what exactly is data availability? What data availability challenges does L2 face? Why does the data availability layer provoke so much controversy in L2? This article will discuss these issues in an attempt to reveal the essence of data availability.

Definition of Data Availability

In short, data availability refers to the ability of block producers to publish all transaction data from a block to the network, allowing validators to download this data.

When the block producers publish complete data and allow validators to download it, we consider the data to be available; conversely, if part of the data is hidden, making it impossible for validators to obtain complete information, the data is considered unavailable.

The difference between data availability and data retrievability

People often confuse data availability and data retrievability, but these two concepts have essential differences:

• Data availability refers to the stage after block production and before consensus is reached, mainly focusing on whether newly released data can pass through consensus.
• Data retrievability refers to the stage after data has been validated by consensus and permanently stored on the blockchain, which is the ability to retrieve historical data.

Industry insiders have pointed out that the term "data availability" may cause misunderstandings and suggest changing it to "data publication" to more accurately reflect its essence.

Data Availability Issues in L2

Although the concept of data availability originated from Ethereum, we are currently more focused on data availability issues at the L2 level.

In L2, the sequencer acts as a block producer and needs to publish sufficient transaction data for validators to verify the validity of transactions. This process faces two main challenges: ensuring the security of the verification mechanism and reducing the cost of publishing data.

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) Ensure the verification mechanism is secure.

OP Rollup and ZK Rollup use different validation methods, but both need to ensure data availability:

• OP Rollup: If the sequencer does not publish the full data, the challenger will be unable to initiate a valid challenge.
• ZK Rollup: Although validity proofs do not require data availability by themselves, it is still necessary to ensure data availability to protect user assets.

Currently, most L2 sequencers choose to publish state data and transaction data on Ethereum to achieve sufficient security.

Reduce the cost of data publication

The Gas fees paid by L2 users are mainly composed of two parts: the Gas for executing transactions on L2 and the Gas for submitting data to L1. Among these, the latter accounts for the majority of the fees, primarily used for publishing transaction data to ensure data availability.

There are two main ways to reduce the cost of data publication:

1. Reduce the cost of publishing data on L1, such as Ethereum's planned EIP-4844 upgrade.
2. Separate the data availability layer from L1, similar to how Rollup strips transaction execution from L1.

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Controversy over Layer 2 Data Availability

The concept of modular blockchain provides a background for understanding the controversy surrounding L2 regarding data availability layers. Modular blockchains decouple the core functions of a blockchain, forming independent modules that enhance performance by combining different specialized networks.

Currently, modular blockchains are typically divided into four layers: execution layer, settlement layer, consensus layer, and data availability layer. L2 has separated the execution layer from Ethereum, but the other three layers still rely on Ethereum.

However, for cost reasons, many L2 projects are considering separating the data availability layer from Ethereum, using Ethereum only as a settlement layer and consensus layer.

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This trend has sparked controversy within the Ethereum ecosystem. Some believe that not using Ethereum as a data availability layer for scaling solutions should not be considered a true L2, as this may not guarantee that operators provide the published data.

This insistence on leaving the data availability layer on Ethereum is ostensibly for security reasons, but it may also reflect concerns about the potential threat to Ethereum's status. After all, if L2 also detaches the data availability layer from Ethereum, it effectively weakens the reliance on Ethereum's security, which could gradually lead away from the Ethereum ecosystem.

Despite these controversies, projects related to data availability layers are still thriving. In the future, we may see more innovative data availability solutions emerge, further driving the development and application of L2 technology.

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