F5 BIG-IP - primary and backup nodes in a pool possible?

Hi all,

On a BIG-IP LTM, is it possible to have members of a pool that would act as "primary" and others that would act as backups?

I want to have a pool that will have at least two members and I'd like all traffic to be sent to a particular node (or nodes) when they are online and only to use other nodes if the "primary" nodes are offline. Is this possible? I looked at the weighted options but it seems there are still instances where traffic can be sent to other nodes even if certain nodes are online.

Thanks