  With the development of blockchain applications, the requirements for file
storage in blockchain are increasing rapidly. Many protocols, including
Filecoin, Arweave, and Sia, have been proposed to provide scalable
decentralized file storage for blockchain applications. However, the
reliability is not well promised by existing protocols. Inspired by the idea of
insurance, we innovatively propose a decentralized file storage protocol in
blockchain, named as FileInsurer, to achieve both scalability and reliability.
While ensuring scalability by distributed storage, FileInsurer guarantees
reliability by enhancing robustness and fully compensating for the file loss.
Specifically, under mild conditions, we prove that no more than 0.1\% value of
all files should be compensated even if half of the storage collapses.
Therefore, only a relatively small deposit needs to be pledged by storage
providers to cover the potential file loss. Because of lower burdens of
deposit, storage providers have more incentives to participate in the storage
network. FileInsurer can run in the top layer of the InterPlanetary File System
(IPFS), and thus it can be directly applied in Web 3.0, Non-Fungible Tokens,
and Metaverse.
