C# FileStream实现大文件复制

public static class FileHelper
 {
  /// <summary>
  /// 复制大文件
  /// </summary>
  /// <param name="fromPath">源文件的路径</param>
  /// <param name="toPath">文件保存的路径</param>
  /// <param name="eachReadLength">每次读取的长度</param>
  /// <returns>是否复制成功</returns>
  public static bool CopyFile(string fromPath, string toPath, int eachReadLength)
  {
   //将源文件 读取成文件流
   FileStream fromFile = new FileStream(fromPath, FileMode.Open, FileAccess.Read);
   //已追加的方式 写入文件流
   FileStream toFile = new FileStream(toPath, FileMode.Append, FileAccess.Write);
   //实际读取的文件长度
   int toCopyLength = 0;
   //如果每次读取的长度小于 源文件的长度 分段读取
   if (eachReadLength < fromFile.Length)
   {
    byte[] buffer = new byte[eachReadLength];
    long copied = 0;
    while (copied <= fromFile.Length - eachReadLength)
    {
     toCopyLength = fromFile.Read(buffer, 0, eachReadLength);
     fromFile.Flush();
     toFile.Write(buffer, 0, eachReadLength);
     toFile.Flush();
     //流的当前位置
    toFile.Position = fromFile.Position;
     copied += toCopyLength;
     
    }
    int left = (int)(fromFile.Length - copied);
    toCopyLength = fromFile.Read(buffer, 0, left);
    fromFile.Flush();
    toFile.Write(buffer, 0, left);
    toFile.Flush();
 
   }
   else
   {
    //如果每次拷贝的文件长度大于源文件的长度 则将实际文件长度直接拷贝
    byte[] buffer = new byte[fromFile.Length];
    fromFile.Read(buffer, 0, buffer.Length);
    fromFile.Flush();
    toFile.Write(buffer, 0, buffer.Length);
    toFile.Flush();
 
   }
   fromFile.Close();
   toFile.Close();
   return true;
  }
 }

class Program
 {
  static void Main(string[] args)
  {
 
   Stopwatch watch = new Stopwatch();
   watch.Start();
   if (FileHelper.CopyFile(@"D:\安装文件\新建文件夹\SQLSVRENT_2008R2_CHS.iso", @"F:\SQLSVRENT_2008R2_CHS.iso", 1024 * 1024 * 5))
   {
    watch.Stop();
    Console.WriteLine("拷贝完成,耗时：" + watch.Elapsed.Seconds+"秒");
 
   }
   Console.Read();
  }
 
 }