In the previous article, we discussed in detail the preparation and transmission of data, mainly introducing two aspects: preparing data for storage, negotiating storage transactions and transmitting data. This article will discuss the question "When to run proof of replication?"

In Proof of Replication , storage miners prove that they are storing a physically unique copy or replicas of the data. Proof of Replication happens only once, when the miner first stores the data.

When storage miners receive each piece of customer data, they put it into a sector. Sector is the basic unit of storage in Filecoin and can contain fragments from multiple transactions and customers. When a sector is filled, a CommD (data commit, also known as UnsealedSectorCID) is generated, representing the root node of all CIDs in the sector.

Next, a process called sealing occurs.

During sealing, the sector data (identified by CommD) is encoded through a series of graphing and hashing to create a unique copy. The root hash of the Merkle tree of the resulting copy is CommRLast. (Learn more about merkle trees in our Decentralized Data Structures tutorial.)

CommRLast is then hashed together with CommC (another merkle root output from the Proof of Replication). This generates CommR (Commitment of Replication, also known as SealedSectorCID), which is recorded to the public blockchain. CommRLast is kept privately by miners for future use in Proof of Spacetime, but is not saved to the chain.

The encoding process is designed to be slow and computationally heavy, so it is difficult to cheat. (Note that encoding is not the same as encryption. If you want to store private data, you must encrypt it before adding it to the Filecoin network.)

CommR provides the proof we need that a miner is storing a physically unique copy of a customer’s data. If you store the same data with multiple storage miners, or make multiple storage deals for the same data with one miner, each deal will have a different CommR.

The sealing process also compresses the proof of replication using zk-SNARKs to keep the chain small so that all members of the Filecoin network can store the chain for verification. We will learn more about zk-SNARKs in future courses.

——End——