Creating a Huge Dummy File in a Matter of Seconds in C#

Question

I want to create a huge dummy file say 1~2 GBs in matter of seconds. here is what I've written in C#:

file.writeallbytes("filename",new byte[a huge number]);

and another way with indicating the status, was like following:

long FSS = din.TotalFreeSpace;
long segments = FSS / 10000;
long last_seg = FSS % 10000;
BinaryWriter br = new BinaryWriter(fs);

for (long i = 0; i < segments; i++)
{
    br.Write(new byte[10000]);

    this.label2.Text = "segments write :" + i.ToString() + "\r\n" + "segments remain :" + ((segments-i)+1).ToString();
    Application.DoEvents();
}
br.Write(new byte[last_seg]);
this.label2.Text += "\r\nDone!";
br.Close();

where din is Disk Information object

well with these two approach it takes something like 2 or more minutes to write such a big but dummy file. Is there any other faster way for doing so?

Answer 1

Simply create the file, seek to a suitably large offset, and write a single byte:

FileStream fs = new FileStream(@"c:\tmp\huge_dummy_file", FileMode.CreateNew);
fs.Seek(2048L * 1024 * 1024, SeekOrigin.Begin);
fs.WriteByte(0);
fs.Close();

This will yield a 2GB file with basically unpredictable contents, which should be fine for your purposes.

Answer 2

If you don't care about the contents, then by far the fastest way I know of is this - it is practically instant:

private void CreateDummyFile(string fileName, long length)
{
    using (var fileStream = new FileStream(fileName, FileMode.Create, FileAccess.Write, FileShare.None))
    {
        fileStream.SetLength(length);
    }
}

Answer 3

If you just need a FileStream, you could use FileStream.SetLength. That will get you a stream which is 2 GB long. Then you can write the final byte at an arbitrary position of your choice. But the contents will be undefined.

If you're trying to actually create a file on the disk, yes, you'll need to actually write its contents. And yes, hard disks are going to be slow; something like a 1 GB/min write speed isn't totally ridiculous. Sorry -- that's physics!

Answer 4

Why did you not use the BackgroundWorker class to achieve this, as you can pass anything into the method ReportProgress to indicate the status report. See the example below:

        private BackgroundWorker bgWorker;
        public Form1()
        {
            InitializeComponent();
            bgWorker = new BackgroundWorker();
            bgWorker.DoWork += new DoWorkEventHandler(bgWorker_DoWork);
            bgWorker.ProgressChanged += new ProgressChangedEventHandler(bgWorker_ProgressChanged);
            bgWorker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bgWorker_RunWorkerCompleted);
            bgWorker.RunWorkerAsync();
        }

        void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
           this.label2.Text = "Done";
        }

        void bgWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
           MyStatus myProgressStatus = (MyStatus)e.UserState;
           this.label2.Text = string.Format("segments write : {0}" + Environment.Newline + "Segments Remain: {1}", myProgressStatus.iWritten, myProgressStatus.iRemaining);
        }

        void bgWorker_DoWork(object sender, DoWorkEventArgs e)
        {
            long FSS = din.TotalFreeSpace;
                long segments = FSS / 10000;
                long last_seg = FSS % 10000;
                BinaryWriter br = new BinaryWriter(fs);

                for (long i = 0; i < segments; i++)
                {
                    br.Write(new byte[10000]);
bgWorker.ReportProgress(i.ToString(), new MyStatus(i, ((segments-i) + 1)));

                }
                br.Write(new byte[last_seg]);
                br.Close();
        }

public class MyStatus{
   public int iWritten;
   public int iRemaining;
   public MyStatus(int iWrit, int iRem){
     this.iWritten = iWrit;
     this.iRemaining = iRem;
   }
}
}

This is a rough draft...

Answer 5

I could be wrong but you will probably find that it's impossible to create a file that large that quickly as there will be a bottleneck in the I/O writing process.

However in your code above the Applciation.DoEvents will be slowing things down. Also any repainting of the screenthis.label2.Text = will cause a slight slow down.