Blob

What Is a Blob?

In the context of blockchain scaling, a blob is a large, cost-effective bundle of data attached to a standard transaction. Blobs were introduced to Ethereum through the EIP-4844 upgrade, also known as Proto-Danksharding. Their primary purpose is to dramatically reduce the cost it takes for Layer 2 rollups to publish their transaction data to the main Ethereum chain.

Before blobs, rollups had to post their data using a field in transactions called CALLDATA. This was expensive because CALLDATA is processed by the Ethereum Virtual Machine (EVM) and stored permanently on the blockchain. Blobs, however, exist in a separate space. They are not processed by the EVM and are only stored temporarily by the network’s nodes, making them a much cheaper alternative.

How Do Blobs Work?

The lifecycle and pricing of blobs are managed through a system designed specifically for data availability, not permanent storage:

Submission

A Layer 2 rollup bundles thousands of its users’ transactions into a single blob. It then creates a special type of transaction on the Ethereum mainnet that includes a commitment (a cryptographic fingerprint) to this blob. The blob itself is broadcast separately across the network.

Temporary Storage

Ethereum’s consensus nodes download and store the full blob, but only for a limited time (e.g., a few weeks). This is long enough for any honest network participant who needs to verify the rollup’s state to access the data. After this period, the blob is deleted from the nodes to save disk space.

Separate Fee Market:

Blobs have their own fee market, distinct from regular Ethereum transactions. The price is determined by supply and demand for blob space, similar to how gas prices work for standard transactions. This separation prevents high demand for rollup data from driving up the cost of regular user transactions on the main chain.

By using blobs, rollups can provide proof to the Ethereum network that all their transaction data was made available, without paying the high cost of permanent on-chain storage. This innovation is a key step in making Layer 2 solutions more scalable and affordable for everyone.