Nobi nobi reservation on hamanasu?

I am planning to take hamanasu on august 6th from aomori to sapporo and on august 12th from sapporo to aomori. Of course with JR railpass.
I read a lot of post aboout hanamasu but i am still wondering if i need a reservation for nobinobi carpet.
If I need reservation how to do it?
Is it OK to buy 2-3 days in advance or do I have to buy it more in advance?
Most important, is nobinobi safe?
Thanks

I read a lot of post aboout hanamasu but i am still wondering if i need a reservation for nobinobi carpet.

Yes, you need a reservation.

If I need reservation how to do it?

Reservations can be made at any JR ticket counter in Japan.

Is it OK to buy 2-3 days in advance or do I have to buy it more in advance?

I think that August 6 will be a very busy day, especially in direction of Sapporo. I am afraid there is a high risk that the nobinobi compartments will be booked out several days in advance.

Likewise, August 12 is within the peak period of the summer holidays and there is a very high risk that the nobi nobi compartments will be booked out. I think they actually already are as of now.

More about the peak of the summer holidays:
http://www.japan-guide.com/e/e2286.html

I strongly recommend to have some alternative plan ready.

Your chance of booking the two rides of nobinobi on the hamanasu will be quite small on the two days. But you can book the "dream car" seats for free on the same train. If the "dream car" seats also not available, there will be non reserve seats although less comfortable comparing to dream car seats.