protected void validate() {
    logger.trace("begin validate.");
    validateClusterName();
    validateUniqueness();
    logger.trace("complete validate.");
  }
Finds Disk by hostname, port, and mount path.

@param hostname of datanode
@param port of datanode
@param mountPath of disk
@return Disk or null if not found.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/HardwareLayout.java