Proof-of-replication (PoRep), often used in reference to Filecoin, is the way that a storage miner proves to the Filecoin (or other) network that they have an entirely unique copy of a piece of data held for the network.
Proof-of-replication acts as a proof-of-retrievability mechanism inside of a proof-of-space mechanism. What does that actually mean? It means that PoRep allows a “prover” to show that they are really and truly using space to store replicas of a piece of information or data. Not only that, but PoRep means that the data that the prover is storing can easily be accessed, aka “retrieved.”
In a proof-of-replication system, participants in the network want to join in as provers and store as much data as they can, because they get network rewards in exchange for their storage space.
Some critics of proof-of-replication systems argue that while the use of proof-of-replication by storage providers creates durability (aka provides the assurance that data will be available even in the case of node failures), PoRep overlooks the fact that the replicated data must be transferred every time a new node is added to the redundancy pool — which can take up bandwidth.