I'm trying to transfer a file over a IHttpHandler, the code is pretty simple. However when i start a single transfer it uses about 20% of the CPU. If i were to scale this to 20 simultaneous transfers the CPU is very high. Is there a better way I can be doing this to keep the CPU lower? the client code just sends over chunks of the file 64KB at a time.

public void ProcessRequest(HttpContext context)
{
      if (context.Request.Params["secretKey"] == null)
      {

      }
      else
      {
           accessCode = context.Request.Params["secretKey"].ToString();
      }

      if (accessCode == "test")
      {
           string fileName = context.Request.Params["fileName"].ToString();
           byte[] buffer = Convert.FromBase64String(context.Request.Form["data"]);
           string fileGuid = context.Request.Params["smGuid"].ToString();
           string user = context.Request.Params["user"].ToString();

           SaveFile(fileName, buffer, user);
      }
}

public void SaveFile(string fileName, byte[] buffer, string user)
{
      string DirPath = @"E:\Filestorage\" + user + @"\";

      if (!Directory.Exists(DirPath))
      {
          Directory.CreateDirectory(DirPath);
      }

      string FilePath = @"E:\Filestorage\" + user + @"\" + fileName;
      FileStream writer = new FileStream(FilePath, File.Exists(FilePath) ? FileMode.Append : FileMode.Create, FileAccess.Write, FileShare.ReadWrite);
      writer.Write(buffer, 0, buffer.Length);
      writer.Close();
}