Performance of java nio with dd in linux.

Question

Hi
I ran this code in java to dump 0s in a file of size 1gb and tried the same with dd in linux.
Java code : I use a preinitialized array (the data) and fill a mappedbytebuffer with it.
package filePersistence.test;
import java.io.File;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class TimeLineTest {
     private static final int BYTE_LENGTH = 1000;
     //this is the input
     static byte[] b = new byte[BYTE_LENGTH];
     public static void main(String[] arg) throws Exception
          //initializing the input
          for (int i=0;i<BYTE_LENGTH;i++)
               b[i] = 0;
          File file = new File(arg[0]);
          RandomAccessFile raFile = new RandomAccessFile(file,"rw");
          FileChannel fChannel = raFile.getChannel();
          int loopCount = 1000000;
          MappedByteBuffer mbuffer = fChannel.map( FileChannel.MapMode.READ_WRITE ,0,loopCount * BYTE_LENGTH);
          //System.out.println(" going to fill in a file" + file.getName());
          long k = 0;
          long startTime = System.currentTimeMillis();
          for (int i=0;i<loopCount;i++)
     //populate the mapped buffer
               mbuffer.put(b);
          //persist into the file
          mbuffer.force();
          long endTime = System.currentTimeMillis();
          System.out.println(" file filled size1 "+file.length());
          System.out.println(" time " + (endTime - startTime));
On a linux machine this takes around 7 secs while dd used as
"dd if=/dev/zero of=mytestfile.out bs=1000 count=1000000"
1000000+0 records in
1000000+0 records out
1000000000 bytes (1.0 GB) copied, 4.618 seconds, 217 MB/s
4.6 and 7 differ quite a lot. Is there a way the java code can be improved to match dd ?(-sever does not help)
Thanks
Sumanta

Answer 1

Hi
Can this be called a dd equivalent code ?
package filePersistence.test;
import java.io.File;
import java.io.FileOutputStream;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
public class TimeLineTest {
     private static final int BYTE_LENGTH = 1000;
     //this is the input
     static byte[] b = new byte[BYTE_LENGTH];
     public static void main(String[] arg) throws Exception
          //initializing the input
          for (int i=0;i<BYTE_LENGTH;i++)
               b[i] = 0;
          String srcFile = arg[0] + "_src";
          FileOutputStream fos = new FileOutputStream(srcFile);
          fos.write(b);
          fos.getFD().sync();
          fos.flush();
          fos.close();
          RandomAccessFile srcraFile = new RandomAccessFile(srcFile,"rw");
          FileChannel srcChannel = srcraFile.getChannel();
          File file = new File(arg[0]);
          RandomAccessFile raFile = new RandomAccessFile(file,"rw");
          FileChannel raChannel = raFile.getChannel();
          int loopCount = 1000000;
          //MappedByteBuffer mbuffer = fChannel.map( FileChannel.MapMode.READ_WRITE ,0,loopCount * BYTE_LENGTH);
          //System.out.println(" going to fill in a file" + file.getName());
          long startTime = System.currentTimeMillis();
          for (int i=0,position=0;i<loopCount;i++,position+=BYTE_LENGTH)
     //populate the mapped buffer
               //mbuffer.put(b);
               raChannel.position(position);
               srcChannel.transferTo(0, BYTE_LENGTH, raChannel);
          //persist into the file
          //mbuffer.force();
          raFile.getFD().sync();
          raChannel.close();
          raFile.close();
          long endTime = System.currentTimeMillis();
          System.out.println(" file filled size1 "+file.length());
          System.out.println(" time " + (endTime - startTime));
}