code: public StorageSize subtract(StorageSize that)
  	{
  		StorageUnit smallestUnit = StorageUnit.smallest(this.getUnit(), that.getUnit());
  
  		final BigInteger a = this.getBits();
  		final BigInteger b = that.getBits();
  		final BigInteger result = a.subtract(b);
  
  		return new StorageSize(smallestUnit, result);
  	}
docs: Subtracts a storage size from the current object, using the smallest unit as the resulting StorageSize's unit
  
  @param storage
  
  @return