@Override
  public MultiByteBuff retain() {
    refCnt.retain();
    return this;
  }
Copy the content from this MBB to a byte[] based on the given offset and length the position
from where the copy should start the length upto which the copy has to be done
@return byte[] with the copied contents from this MBB.
hbase-common/src/main/java/org/apache/hadoop/hbase/nio/MultiByteBuff.java