Directory file size calculation - how to make it faster?

Question

Using C#, I am finding the total size of a directory. The logic is this way : Get the files inside the folder. Sum up the total size. Find if there are sub directories. Then

Answer 1

Based on the answer by spookycoder, I found this variation (using DirectoryInfo) at least 2 times faster (and up to 10 times faster on complex folder structures!) :

    public static long CalcDirSize(string sourceDir, bool recurse = true)
    {
        return _CalcDirSize(new DirectoryInfo(sourceDir), recurse);
    }

    private static long _CalcDirSize(DirectoryInfo di, bool recurse = true)
    {
        long size = 0;
        FileInfo[] fiEntries = di.GetFiles();
        foreach (var fiEntry in fiEntries)
        {
            Interlocked.Add(ref size, fiEntry.Length);
        }

        if (recurse)
        {
            DirectoryInfo[] diEntries = di.GetDirectories("*.*", SearchOption.TopDirectoryOnly);
            System.Threading.Tasks.Parallel.For(0, diEntries.Length, () => 0, (i, loop, subtotal) =>
            {
                if ((diEntries[i].Attributes & FileAttributes.ReparsePoint) == FileAttributes.ReparsePoint) return 0;
                subtotal += __CalcDirSize(diEntries[i], true);
                return subtotal;
            },
                (x) => Interlocked.Add(ref size, x)
            );

        }
        return size;
    }