read/write bytes in chunks

I have this code zipping files, directories, subdir/files, etc successfully - almost.
When I get to a large file, I get the error "Arithmetic operation resulted in an overflow". Based on what I've read, my zFileBuffer is larger than As Byte can handle and I need to read and write the bytes in chunks, say 1024. I'm very much a beginner, can someone please help adjust my code to read/write bytes so I don't overload the byte buffer?
Many, many, many thanks.

Private Sub Zip(ByVal SourceFolder As String, ByVal DestFile As String)
 
        Dim DirFileNames() As String = Directory.GetFiles(SourceFolder, "*", SearchOption.AllDirectories)
        Dim objCrc32 As New Crc32()
        Dim zipStream As ZipOutputStream
 
        zipStream = New ZipOutputStream(File.Create(DestFile))
        zipStream.SetLevel(9) 
 
        Dim zFile As String
 
        For Each zFile In DirFileNames
            Dim zFileStream As FileStream = File.OpenRead(zFile)
            Dim zFileBuffer(zFileStream.Length - 1) As Byte
 
            Dim strSource As Integer = SourceFolder.Length + 1
 
            zFileStream.Read(zFileBuffer, 0, zFileBuffer.Length)
            Dim objZipEntry As ZipEntry = New ZipEntry(zFile.Substring(strSource))
 
            objZipEntry.DateTime = DateTime.Now
            objZipEntry.Size = zFileStream.Length
            zFileStream.Close()
            objCrc32.Reset()
            objCrc32.Update(zFileBuffer)
            objZipEntry.Crc = objCrc32.Value
            zipStream.PutNextEntry(objZipEntry)
            zipStream.Write(zFileBuffer, 0, zFileBuffer.Length)
 
        Next
 
        zipStream.Finish()
        zipStream.Close()
 
    End Sub

Select allOpen in new window