Filling a large Array with random Bytes

[Devon_Nullman]

I am creating a Hard Drive Eraser using normal Filesystem calls, it repeatedly writes files until the disk is 100% full. I wold like the option to fill the write buffer with random bytes but am getting out of memory exceptions trying to fill a 1 Gig buffer. I have sort of fixed that but I still see out of memory when I change from 1GB to 512MB and back to 1GB - Looping through the array works fine but is agonizingly slow. Have a look at my sample app please and any suggestions would be great. Using much smaller files avoids this but I don't want to leave a 4 TB drive with tens of thousands of files if possible.

Form Layout:



Code:

Option Strict On
Imports System.Security.Cryptography

Public Class Form1
Private Sizes As New List(Of Integer)
Private SizeText As New List(Of String)
Private Filesize As Integer = 0
Private RNG As New RNGCryptoServiceProvider
Private R As New Random
Private Buffer(1) As Byte
Private SW As New Stopwatch

Private Function ShowFriendlyNumber(ByVal number As Long) As String
Dim TB As Long = 1024L * 1024L * 1024L * 1024L
Dim GB As Long = 1024L * 1024L * 1024L
Dim MB As Long = 1024L * 1024L
Dim KB As Long = 1024L
ShowFriendlyNumber = "0"
If number > TB Then
Return Format((number / TB), "F2") & " TB"
ElseIf number > GB Then
Return Format((number / GB), "F2") & " GB"
ElseIf number > MB Then
Return Format((number / MB), "F2") & " MB"
ElseIf number > KB Then
Return Format((number / KB), "F2") & " KB"
Else
Return number.ToString & " Bytes"
End If
End Function

Private Sub DisplayBuffer(Method As String)
TxtResults.Text = "Buffer Size = " & ShowFriendlyNumber(Buffer.Length) & " - Took " &
SW.Elapsed.ToString & " Using " & Method & vbNewLine
TxtResults.AppendText("First 100 Bytes:" & vbNewLine)
For I = 0 To 99
TxtResults.AppendText(Buffer(I).ToString("X2") & " ")
Next
TxtResults.AppendText(vbNewLine & vbNewLine & "Last 100 Bytes" & vbNewLine)
For I = Buffer.Length - 100 To Buffer.Length - 1
TxtResults.AppendText(Buffer(I).ToString("X2") & " ")
Next
End Sub

Private Sub Form1_Shown(sender As Object, e As EventArgs) Handles Me.Shown
Sizes.AddRange({1, 64, 128, 256, 512, 1024})
SizeText.AddRange({"1 MiB", "64MiB", "128 MiB", "256 MiB", "512 MiB", "1 GiB"})
CBSize.Items.Clear()
CBSize.Items.AddRange(SizeText.ToArray)
CBSize.SelectedIndex = 0
End Sub

Private Sub CBSize_SelectedIndexChanged(sender As Object, e As EventArgs) Handles CBSize.SelectedIndexChanged
Filesize = Sizes(CBSize.SelectedIndex) * 1024 * 1024 - 1
End Sub

Private Sub BtnUseCrypto_Click(sender As Object, e As EventArgs) Handles BtnUseCrypto.Click
Try
SW.Reset()
SW.Start()
If Buffer.Length <> Filesize + 1 Then
ReDim Buffer(Filesize) ' Seems to fix using 1GiB multiple times - 512Mib to 1GiB still errors
End If
RNG.GetBytes(Buffer) 'Exception Always HERE
SW.Stop()
DisplayBuffer("Crypto")
Catch ex As Exception
TxtResults.Text = "Exception - " & ex.Message & ex.StackTrace & vbNewLine
End Try

End Sub

Private Sub BtnOnebyOne_Click(sender As Object, e As EventArgs) Handles BtnOnebyOne.Click
SW.Reset()
SW.Start()
ReDim Buffer(Filesize)
For I As Integer = 0 To Buffer.Length - 1
Buffer(I) = CByte(R.Next(0, 256))
Next
SW.Stop()
DisplayBuffer("Looping")
End Sub
End Class



On my system, a 1 GB buffer takes 10 sec using the Crypto Library and 40 seconds using the loop. I'd really prefer something even faster even if it isn't Cryptographically secure so I could fill each file with different data. See the bold text in the code.

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