I got recently new hdds (7200rpm) and they get very hot. I have a chassis like this where the hdds are placed sideways. On the side is a fan case for 3 fans.
In which direction should they point?
Into the case and blow cold air in?
Or point outside the cas and blow hot air coming from the hdds out?
I know that in normal cases you would blow the air in the front in and get the hot air out of the case with exhaust fans|the psu.
Pic related looks like my pc case.
And another picture with the chassis closed. As you can see there are holes in the side panel from where the cold air could be sucked in if the fans blow air out on the other side.
It's really up to you and how you want your setup to work. Consider the other fans in the case and which way they are all facing too.
A lot of people try to have more fans going in than out, therefore creating a net positive pressure inside the case, hopefully not sucking in dust in any gaps.
Either way just think about the fans you have and where you want the air to flow and go from there. Up to you
It makes almost no difference for cooling, with blowing in having a slight edge.
But blowing in has the distinct advantage of more intake than outtake in the case, giving it ever so slight positive pressure and preventing tons of dust within case.
(you obviously still need some form of dust filters on intake)