Are you referring to VSF Links between Aruba 5400R zl2 or are you referring to uplinks/downlinks to access Switches or Servers?
If you refer to uplinks/downlinks to access Switches or Server, the best practice - remember you're running two Chassis in a VSF - is to "dual homing" all the links: so each switch/server uplinked to VSF should have a leg (or legs) on the 1st VSF Member and the other leg (or legs) on the 2nd VSF Member.
VSF Link(s) between VSF Members are, always following best practice, generally deployed using two or more links at 10G or 40G (generally via DAC cables since VSF Members are very near each others).
If you need some VSF related documentation I can post you some interesting links so you can understand VSF related requirments/restrictions.