Yes, two packets of yeast are required for lagers because you're fermenting at a lower temperature and yeast metabolism slows down quite a bit in colder environments, therefor you increase the size of your pitch rate to make up for the difference so you don't have any off flavors - diacetyl being the biggy.
Personally, I use 34/70 quite a bit - and if I'm not repitching I use two packets and have never had an issue. I ferment my pilsners at around 50. I don't do a diacetyl rest and I've never had an issue. When I pitch liquid yeast I use a minimum of 1.5 liters of slurry for each 5 gallons. 34/70 is a great yeast if that's the one you're using - I've never had a bad lager with it.