Blockweave

Blockweave is the data structure used by the Arweave network, which is designed to store data permanently. Like a blockchain, it links each new block to the one before it. In addition, each block is linked to a randomly selected earlier block, called the recall block. To produce a new block, miners must prove they have access to data from that earlier block, which rewards them for storing as much of the network's history as possible.

The design lets Arweave operate as a decentralized storage network in which users pay once to store data that is meant to remain available indefinitely. It contrasts with the Bitcoin blockchain and others that require every full node to hold the entire history, and with storage networks such as Filecoin, which use time-limited storage contracts. Arweave launched in 2018 and has been used to store websites, NFT files, archives and records, forming what its developers call the "permaweb".

Imagine a library that wants every book kept forever, but cannot afford to make every librarian keep a copy of every book. So it sets a rule: to earn your wage each day, you must show the manager a page from a randomly chosen old book. Since you never know which book will be picked, the safest strategy is to keep as many books as possible, and especially the rare ones that few others hold.

Arweave's blockweave works the same way. Miners are paid for adding new blocks, but only if they can prove they hold a random piece of old data. Over time, this encourages many miners to store copies of the whole archive, so data remains retrievable even if some miners leave.

Each Arweave block contains references to:

• The previous block. As in a normal chain, this fixes the order of history.
• A recall block. An earlier block selected through a deterministic random process based on the previous block's data.
• Stored data. New files or transactions submitted by users, with their content addressed by a hash.

The original consensus mechanism, Proof of Access, required miners to include data from the recall block in their work. It was later refined into a system based on succinct proofs of random access, which rewards miners who can retrieve stored data quickly, discouraging them from fetching it from others on demand. Each piece of content is identified by its hash, so anyone retrieving it can check that it has not been altered. Because nodes are not required to store everything, the network relies on incentives rather than rules to ensure enough copies exist.

Users pay a one-time fee in the network's AR token to store data, a cost that moves with the token's price and with the volatility of crypto markets. Most of each payment goes into an endowment that pays miners over time. The model assumes that the cost of storing data falls over the long term, as it has historically, so that the endowment can cover storage for a very long period, which the project describes as around 200 years under conservative assumptions. Critics note that this depends on continued declines in storage cost and on the token keeping enough value, both of which are uncertain. The model differs from cloud storage, which charges monthly, and from the InterPlanetary File System, which addresses content but does not itself pay anyone to keep it.

Arweave is used to store data that people want to remain available and unchanged, including:

• NFT media. Images and metadata for NFTs, so they do not depend on a company's server.
• Web pages and apps. Static websites and front-ends for decentralized applications that cannot be easily taken down.
• Archives. News articles, research papers, public records and social media posts preserved against deletion.
• Blockchain data. Some networks store historical data or snapshots on Arweave.

In 2024 the Arweave team introduced AO, a computing system that uses Arweave as its data layer, extending the network beyond storage.

Permanent storage raises legal and ethical questions. Data written to the blockweave cannot easily be deleted, which conflicts with rights to erasure in laws such as the GDPR and with requests to remove illegal or harmful content. Individual miners can choose not to store or serve certain content, using content policies, but the data may persist elsewhere. The long-term economics depend on assumptions that cannot yet be tested, and the price of the AR token is volatile like other crypto assets. Retrieval speed and reliability depend on gateways that serve data to ordinary web users, some of which are centralized. As with other decentralized storage networks, users should consider privacy before uploading anything, since public data on the blockweave is visible to all. Broader questions about permanence are discussed under immutability.

• Arweave