code: public byte[] keyToStorageFormat(byte[] key) {
  
          switch(getReadOnlyStorageFormat()) {
              case READONLY_V0:
              case READONLY_V1:
                  return ByteUtils.md5(key);
              case READONLY_V2:
                  return ByteUtils.copy(ByteUtils.md5(key), 0, 2 * ByteUtils.SIZE_OF_INT);
              default:
                  throw new VoldemortException("Unknown read-only storage format");
          }
      }
docs: Converts the key to the format in which it is stored for searching
  
  @param key Byte array of the key
  @return The format stored in the index file