DVR Fan

Hi My DVR-508--K1 installed a few days ago is set to record 24/7. The fan is constantly whirring round.
Question. Is this OK and if I go away for couple of weeks, is this safe? It is ventilated.
Question. Is ok to leave it on 24/7 record or is record on Motion only better. I do have many motion notifications as the birds/flies etc are picked up and I have sensitivity turned down, but yet to find out

Thanks Guys