VB.NET Speed up cycle function - vb.net

Question

I have this function to write bytes in a bin file.
Public Shared Function writeFS(path As String, count As Integer) As Integer
Using writer As New BinaryWriter(File.Open(path, FileMode.Open, FileAccess.Write, FileShare.Write), Encoding.ASCII)
Dim x As Integer
Do Until x = count
writer.BaseStream.Seek(0, SeekOrigin.End)
writer.Write(CByte(&HFF))
x += 1
Loop
End Using
Return -1
End Function
I have a textBox that is the count value. Count is the number of byte to write into the file.
The problem is when i want to write 1mb+ it take like 10+ seconds because of the cycle.
I need a better/faster way to write hex value FF at the end of file 'value' times.
I'm sorry if i've not explained very well.

Answer 1

This should be better:
Public Shared Function writeFS(path As String, count As Integer) As Integer
Using writer As New BinaryWriter(File.Open(path, FileMode.Open, FileAccess.Write, FileShare.Write), Encoding.ASCII)
Dim x As Integer
Dim b as Byte
b = CByte(&HFF)
writer.BaseStream.Seek(0, SeekOrigin.End)
Do Until x = count
writer.Write(b)
x += 1
Loop
End Using
Return -1
End Function
That way you're not calling CByte every time. And there is no need to move to the end of the stream after each write.

Answer 2

Some questions before:
Why is the function Shared? Why do you use FileSHARE.Write? WriteShare means that OTHER process can write to the file, while YOU write to it. And WHY do you write single bytes that are all the same? And why does the function return -1 every time? Might be better fitter with a SUB? And why not using a simple for loop instead while?
Public Sub writeFS(path As String, count As Integer)
Using Stream As New FileStream("", FileMode.Append, FileAccess.Write, FileShare.Read)
Stream.Write(Enumerable.Repeat(Of Byte)(255, count).ToArray, 0, count)
End Using
End Sub
OK, if you need to write 100MB, this doesnt fit, but than you can partition your writes.