The three major decentralized storage cryptocurrencies are Arweave, Filecoin, and Storj.

Arweave

Arweave focuses on long-term or permanent storage, using a one-time payment model. It employs 'blockweave' technology, where each new block contains references to earlier random blocks, encouraging the long-term preservation of data. Users pay a one-time fee for data storage, and the data can theoretically be accessed permanently.

Filecoin

Filecoin aims to create a decentralized storage market similar to traditional cloud storage services. It uses 'proof of storage' and 'proof of spacetime' to ensure data is stored correctly. Filecoin targets the professional market, offering flexible storage needs.

Storj

Storj focuses on providing decentralized cloud storage services that ensure security and privacy protection. Its token is an ERC20 token issued on Ethereum, but Storj itself is not a blockchain project; it operates through a centralized reward mechanism, distributing rewards each month based on the storage capacity of individual miners.