file close시 오랜시간이 걸립니다. 왜 그럴까요?

        #define BURST_SIZE	136314880
 
	printf("%s write perfermance \n", argv[1]);
	if ((ifd = open(argv[1], iflag)) < 0) {
		printf("open %s fail \n", argv[1]);
		return -1;
	}
 
	stick = get_tick_count();
	for(i=0; i<LOOP_COUNT; i++) {
		full_write(ifd, buf, BURST_SIZE);
	}
	stick1 = get_tick_count();
	close(ifd);
	etick1 = get_tick_count();
	printf("%d ms\n", etick1 - stick1);
 
	etick = get_tick_count();	
	printf("elapsed time : %dms  size: %dMB  speed : %dMB/s\n\n", 
		etick-stick, 
		(BURST_SIZE/(1024*1024))*LOOP_COUNT, 
		((BURST_SIZE/1000)*LOOP_COUNT)/(etick-stick));