In some embodiments, a method sends first messages that request first information for a set of blocks of the blockchain to the N replicas. Each replica maintains a respective instance of the blockchain. Second messages is received from at least a portion of the N replicas. The second messages include the first information for the set of blocks from each respective instance of the blockchain that is maintained by the N replicas. The method analyzes the first information to determine whether a consensus on the first information is reached by a number of replicas. When consensus is reached, a request is sent to a replica for one or more blocks to back up to a backup blockchain and second information is received for the one or more blocks from the replica. The method uses the second information to back up the one or more blocks in the backup blockchain.