Для Гуру - генерация рандомных символов

char[] symbolss = "ABCDEFGHIGKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789".ToCharArray();
            ThreadLocal<Random> rnd = new ThreadLocal<Random>(() => new Random(Guid.NewGuid().GetHashCode()));
            ConcurrentQueue<string> queRnd = new ConcurrentQueue<string>();
            Parallel.For(0, 10000000, (i) =>
            {
                StringBuilder sb = new StringBuilder(50);
                sb.Append('S');
                for (int j = 0; j < 29;j++)
                {
                    sb.Append(symbolss[rnd.Value.Next(0, 62)]);
                }
                queRnd.Enqueue(sb.ToString());
            });

 project.SendInfoToLog("start");

List<string> buf = new List<string>();
string str = "SAEIOUYBCDFGHJKLMNPQRTVWXZaeiouybcdfghjklmnpqrstvwxz1234567890";
char[] chars = str.ToCharArray();

StringBuilder sb = new StringBuilder();
var rnd = new Random();

for(int a = 0; a < 8; a++)
{
    for(int b = 0; b < 10000000; b++)
    {
        for(int c = 0; c < 30; c++)
        {
            if(c == 0)
                sb.Append(chars[0]);
            else
                sb.Append(chars[rnd.Next(0,62)]);
        }
        buf.Add(sb.ToString());
        sb.Clear();
    }
   
    int unixTime = (int)(DateTime.UtcNow - new DateTime(1970, 1, 1)).TotalSeconds;
   
    string path = project.Directory + @"\\DATA\\" + unixTime.ToString() + @".txt";
   
    FileInfo fileres = new FileInfo (path);
    System.IO.File.WriteAllLines(path, buf);
   
    buf.Clear();
}

project.SendInfoToLog("STOP");