is it ok to mout the drobo sideways? - I am assuming that it is, but just want to make sure.
NO, it’s not ok.
You wanted it mounted the way it’s pictured. Drives are sideways not on top of each other.
You can damage the backplane where the drives connect if you have its sideways.
I’d also suggest if they had intended it to be mountable sideways, they would have put feet on the side, or given it a stand, like with external hard disks
Drobo Pro and Drobo Elite have drives vertical (sideways).
Drobo, Drobo S, Drobo FS have drives horizontal (flat).
Either way, it is not safe to run any Drobo unit in any orientation other than its standard orientation.
Because Drobo drive bays don’t use carrier trays/rails, there are some physical conditions that need to be met for things to line up, because of that funny thing called gravity.
got it.!! - won’t mount it sideways then it would have looked very nice next to my MacPro
buy two drobo S and stack them