My app creates a 2GB file and needs to select the fastest drive on the system with enough space. I am trying to calculate throughput by creating the file, setting the length, then writing data to it sequentially as follows:
FileInfo file = null;
var drives = DriveInfo.GetDrives();
var stats = new List<DriveInfoStatistics>();
foreach (var drive in drives)
{
do
{
file = new FileInfo(Path.Combine(drive.RootDirectory.FullName, Guid.NewGuid().ToString("D") + ".tmp"));
}
while (file.Exists);
try
{
using (var stream = file.Open(FileMode.CreateNew, FileAccess.Write, FileShare.None))
{
var seconds = 10;
var frameRate = 120F;
var bytesWritten = 0L;
var bytesPerPixel = 1;
var watch = new Stopwatch();
var videoSize = new Size(1328, 1048);
var buffer = new byte [(int) (videoSize.Width * videoSize.Height * bytesPerPixel)];
stream.SetLength((long) (videoSize.Width * videoSize.Height * bytesPerPixel * frameRate * seconds));
watch.Restart();
for (int i = 0; i < seconds; i++)
{
for (int j = 0; j < frameRate; j++)
{
stream.Write(buffer, 0, buffer.Length);
bytesWritten += buffer.Length;
}
}
watch.Stop();
stats.Add(new DriveInfoStatistics(drive, bytesWritten / watch.Elapsed.TotalSeconds));
}
}
catch
{
}
finally
{
file.Refresh();
if (file.Exists) { try { file.Delete(); } finally { file.Refresh(); } }
}
}
if (stats.Count == 0)
{
throw (new Exception("No suitable drives were found."));
}
else
{
stats.Sort((x, y) => y.DataTransferRate.CompareTo(x.DataTransferRate));
message
= "The following drives are suitable candidates (best to worst):"
+ Environment.NewLine
+ Environment.NewLine
+ string.Join(Environment.NewLine, stats.ConvertAll<string>(s => (s.DriveInfo.RootDirectory.FullName.Substring(0, 2).ToUpper() + " " + ConversionUtilities.ToIsuBytesNotation(s.DataTransferRate) + "ps")))
+ Environment.NewLine
+ Environment.NewLine
+ "Test results may vary based on other applications accessing the drives."
+ Environment.NewLine
+ Environment.NewLine
+ "Try the test with the system configured as it would be in production."
;
MessageBox.Show(message);
}
The results I am getting make no sense:
DESKTOP
D: 4.15 GBps // SSD.
F: 4.09 GBps // HDD (5200 RPM).
E: 4.06 GBps // HDD (7500 RPM).
C: 4.03 GBps // SSD.
H: 2.45 GBps // Ram Disk!!!
- First of all, the SSDs and HDDs are too close together.
- Secondly, the speeds are much faster than I would expect.
- Thirdly, the Ram Disk (created with RAMDisk) seems to have the lowest throughput. In practice, the Ram Disk outperforms others by far when writing actual video data.
LAPTOP
E: 981.24 MBps // Ram Disk.
C: 100.17 MBps // HDD (5200 RPM).
D: 055.94 MBps // HDD (5200 RPM).
The results of the same code on my development laptop are more believable.
Is there something wrong with the code above? If not, how would you explain a throughput of 4 GBps for an SSD while the Ram Disk tops out at 2.5 GBps?
I understand there are many factors affecting throughput and that benchmarking software is very sophisticated. However, in my case writing a 2GB video file at 120 frames per second without losing frames is crucial and the above code is supposed to present the user with a quick and dirty recommendation on which drive to use to hold transient video frames. The frames are later post-processed and transcoded into an MP4 video only a few megabytes in size.
Lastly, I have tried the above code alongside Contig.exe from Sysinternals to ensure a contiguous layout for better HDD performance. However, I did not notice a difference in performance which indicates that the file was not fragmented enough to begin with (upon creation).
