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copied!<p>Too much code to put in a comment - the short answer is that Exists + Write should generally take longer than just write (even for existing files). </p> <p>Disk IO is not very predictable (caching, warm-up, machine load, IO queues, HDD/SSD model, etc) but running tests with a large number of iterations (more than 1000) that take more than a few ms should give you and idea. On my machine, Exists+Write generally take longer but there are exceptions too - it could be a page swap interfering or one of the VMs, who knows....</p> <p>Here's a slightly modified test suite with 4 scenarios: 1. new folder, write only 2. new folder, exists + write 3. existing folder and files (from step 2) write only 4. existing folder and files (from step 2) exists + write </p> <p>Code below:</p> <pre><code>class FTest { static string myPath = "C:\\Users\\DRook\\Desktop\\temp\\"; static string myPathFile = myPath + "file"; public static void test() { for (int i = 0; i < 5; i++) { DoSomeWork(); Console.WriteLine(" = = = = = =============== = = = = ="); } Console.ReadKey(); } public static void testX1(string path, int index) { using (StreamWriter sw = new StreamWriter(path + index.ToString() + ".txt")) { sw.Write(index.ToString()); } } public static void testX2(string path, int index) { if (!File.Exists(path + index.ToString() + ".txt")) { using (StreamWriter sw = new StreamWriter(path + index.ToString() + ".txt")) { sw.Write(index.ToString()); } } else { using (StreamWriter sw = new StreamWriter(path +"n"+ index.ToString() + ".txt")) { sw.Write(index.ToString()); } } } static void runTestMeasure(Action<string, int> func, int count, string message, bool cleanup) { if (cleanup) { if (Directory.Exists(myPath)) Directory.Delete(myPath, true); System.Threading.Thread.Sleep(500); Directory.CreateDirectory(myPath); System.Threading.Thread.Sleep(500); } System.Diagnostics.Stopwatch stopWatch = new System.Diagnostics.Stopwatch(); stopWatch.Start(); for (int i = 0; i < count; i++) { func(myPath,i); } stopWatch.Stop(); Console.WriteLine(message+": " + stopWatch.Elapsed); } static void DoSomeWork() { int count = 10000; runTestMeasure((path, ndx) => { testX1(path, ndx); },count,"Write missing file",true); System.Threading.Thread.Sleep(5000); runTestMeasure((path, ndx) => { testX2(path, ndx); }, count, "Write+Exists missing file",true); System.Threading.Thread.Sleep(5000); runTestMeasure((path, ndx) => { testX2(path, ndx); }, count, "Write existing file", false); System.Threading.Thread.Sleep(5000); runTestMeasure((path, ndx) => { testX2(path, ndx); }, count, "Write+Exists existing file", false); } } </code></pre> <p>Check for yourself and see how it behaves on your machine. BTW: no point in having <code>i++;</code> inside for loops.</p> <p>Edit: fixed <code>textX2</code> code to create new file (alternate name) if file exists</p>

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