FileStream Read 怎麼清空緩存呀

USB2.0閃盤,讀一個64MB的文件,第一次讀大概是4s左右,第一次以後,就只要0.1s了,初步懷疑是沒有清空緩存,但不知道在哪裡清空,請高手指點...謝謝!



DateTime StartTime,EndTime;

long FileSize;

double TestTime;

StartTime = DateTime.Now;



                string strPath = string.Format(@"{0}{1}", Volume, FullFileName);

                if (!File.Exists(strPath))

                    throw new Exception(string.Format("{0} 文件不存在,請先進行寫入測試!", strPath));

                FileInfo f = new FileInfo(strPath);

                FileSize = f.Length;

                using (FileStream fs = new FileStream(strPath, FileMode.Open, FileAccess.Read, FileShare.None))

                {

                    int length = (int)FileSize;

                    byte[] readBuf = new byte[FileSize];

                    int count;

                    int sum = 0;              

                    while ((count = fs.Read(readBuf, sum, length - sum)) > 0)

                        sum += count;

                    EndTime = DateTime.Now;

                    fs.Close();

                    readBuf = null;

                }

                GC.Collect();

                TestTime = (EndTime - StartTime).TotalMilliseconds;

usb 异常

补充：.NET技术 ,  C#