1. A method for a content item block replication protocol, the method performed by an on-premises block server comprising one or more processors and memory, the method comprising: receiving, from a metadata server of an online content management service by a data network communicatively coupling the on-premises block server to the metadata server, an identification of content item blocks, wherein a content item, hosted with the online content management service, comprises the content item blocks; based, at least in part, on the received identification, storing a replication log entry in a replication log, the replication log entry comprising the identification of content item blocks and an identifier of a peer on-premises content item block server; based, at least in part, on processing the replication log entry, transmitting, to the peer on-premises content item block server identified in the replication log entry by a data network communicatively coupling the on-premises block server and the peer on-premises block server, an offer to send at least one content item block, of the content item blocks of which the content item is composed, to the peer on-premises content item block server identified in the replication log entry; receiving, from the peer on-premises content item block server by the data network communicatively coupling the on-premises block server and the peer on-premises block server, an acceptance of the offer to send the at least one content item block; and based, at least in part, on the received acceptance, sending, by the data network communicatively coupling the on-premises block server and the peer on-premises block server, the at least one content item block to the peer on-premises content item block server.