@Override
  protected void prepareBuffer() {
    super.prepareBuffer();
    bufferToSend.writeShort(VERSION_V1);
    bufferToSend.writeShort(numReplicasCaughtUpPerPartition);
    bufferToSend.writeByte((byte) storeControlAction.ordinal());
  }
@return the least number of replicas that have to be within 0 byte for each partition.
ambry-protocol/src/main/java/com/github/ambry/protocol/BlobStoreControlAdminRequest.java