为什么linux命令(iostat)中的每秒读取数(r / s)始终为零？

我运行一个 java代码,它会从文本文件中生成大量的读写内容.程序源非常简单,在循环中我在测试文件中写入2000行,然后我再次读取它们只是为了生成大量的磁盘读写.但是当程序运行时,我通过“iostat -d -x 1”监视磁盘我发现第二个“r / s”中的读取没有变化但是“w / s”增加了我的预期！
这是iostat命令的示例输出：

Device: rrqm/s wrqm/s  r/s   w/s    rsec/s wsec/s   avgrq-sz avgqu-sz await svctm  %util
sda     0.00   913.00  0.00  82.00  0.00   7872.00   96.00    0.58    7.09   7.11  58.30

Device: rrqm/s wrqm/s  r/s   w/s   rsec/s  wsec/s  avgrq-sz  avgqu-sz  await  svctm  %util
sda     0.00   869.00  0.00  79.00  0.00   7584.00    96.00   0.57    7.11   7.18  56.70

Device: rrqm/s wrqm/s  r/s   w/s   rsec/s  wsec/s  avgrq-sz avgqu-sz   await  svctm  %util
sda     0.00   847.00  0.00  77.00  0.00   7392.00   96.00   0.57      7.42   7.43  57.20

Device: rrqm/s wrqm/s  r/s   w/s   rsec/s  wsec/s   avgrq-sz avgqu-sz  await  svctm  %util
sda     0.00  1221.00  0.00  113.00  0.00  10760.00  95.22    0.84     7.47   7.32  82.70

如图所示,所有“r / s”都为零！但在Java程序中,我读到的文件和我在文件中写的一样多吗？！当我运行Java代码时,每秒写入次数增加,但“r / s”没有变化!!
这是我在监视磁盘时运行的java代码：

import java.io.*;

public class Test {

    public static void main(String [] args) throws IOException{

    String fileName = "/scratch/dump_file.txt";
    File f = new File(fileName);
    // Attempt to delete it
    boolean success = f.delete();
    int j=0;
    while(j<20000)
    {
        ++j;
        Writer output = null;
        String text = "A test content";
        File file = new File(fileName);
        output = new BufferedWriter(new FileWriter(file));

        int i=1;
        while(i<2000)
        {
            //Here we start writing 2000 lines into file line by line
            output.write("j==="+Integer.toString(j)+text+Integer.toString(i)+"n");
            ++i;
        }
        output.close();
        System.out.println("Your file has been written");  

        String line = null;
        try {
            // FileReader reads text files in the default encoding.
            FileReader fileReader = new FileReader(fileName);
            BufferedReader bufferedReader = 
            new BufferedReader(fileReader);
            i=1;
            while((line = bufferedReader.readLine()) != null) {
                //Here we start reading from file line by line and show the result on screen
                ++i;
                System.out.println(line);
            }   
            // Always close file
            bufferedReader.close();         
        }
        catch(FileNotFoundException ex) {
            System.out.println(
                "Unable to open file '" + 
                fileName + "'");                
        }
        catch(IOException ex) {
            System.out.println(
                "Error reading file '" 
                + fileName + "'");                  
            // Or we could just do this: 
            // ex.printStackTrace();
        }
    }
}
}