This question pops up in various forums every once in a while. Essentially, someone would call Directory.GetFiles with something like “*.dat” and would be annoyed to find that *.dat matches .dat, .data, and even .date. Not what they wanted.
Unfortunately, this is by design. You have to do post-filtering to select just the files you want.
var files = Directory.GetFiles(@"d:\tmp", "*.dat").Where(
s => s.EndsWith(".dat"));
The reason it works this way is most likely for backward compatibility with the old 8.3 file system. And it’s really not a .NET restriction here, it’s an API restriction. Both FindFirstFile and FindNextFile have this behavior and it’s these API calls that are P/Invoked by Directory.GetFiles.
Nish Nishant's technology blog 
You can call me a Nigromant if you want, but I was trying to deal with Directory.Getfiles thing to get a Directory (and sub directory) size. I have a code like this:
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim PDRFolder As New DirectoryInfo(“C:\InputMedia”)
Dim filesInfo9() As FileInfo = PDRFolder.GetFiles(“*.*”, SearchOption.AllDirectories)
Dim fileSizePDR As Long = 0
Dim fileSize9 As Long = 0
‘Inicia el calculo de consumo para Playout PDR Folder
For Each fileInfo9 As FileInfo In filesInfo9
fileSize9 += fileInfo9.Length
Next
fileSizePDR = fileSize9
lblBytes_PDR.Text = fileSizePDR.ToString
lblSize_PDR.Text = FormatNumber(fileSizePDR / (1024 * 1024 * 1024), 2) + ” GB” + ” (” + lblBytes_PDR.Text + ” bytes)”
lblFolder_PDR.Text = PDRFolder.ToString
lblHours_PDR.Text = CStr(FormatNumber((fileSizePDR / (1024 * 1024 * 1024)) / 15, 2))
‘Conversion a formato de tiempo para Playout PDR Folder
Dim value9 As Decimal = lblHours_PDR.Text
Dim ts9 As TimeSpan = TimeSpan.FromHours(value9)
Label5.Text = (String.Format(“{0}h {1}m {2}.{3}s”, ts9.Hours, ts9.Minutes, ts9.Seconds, ts9.Milliseconds))
hor5 = fileSizePDR
‘Fin del calculo de consumo para Playout PDR Folder
If Val(lblSize_PDR.Text) > 700 Then ‘value in GB
pbPDR.Visible = True ‘Muestra la alarma en caso el tama;o sea mayor
tbLog.Text &= System.DateTime.Now.ToString & vbCrLf
tbLog.Text &= “Límite de almacenamiento superado en PDR” & vbCrLf
tbLog.SelectionStart = tbLog.TextLength
tbLog.ScrollToCaret()
Else
pbPDR.Visible = False
End If
End Sub
But it has a poorly performance. I have to check 5 differents directories that has in total about 5 TB.
This is a net framework 2 target project. Can you help me to improve this code?