In 9.x we introduced the concept of "Profiles" which are basically ways to group similar pieces of configuration on an object so that you can reuse them on multiple objects. In 9.x persistence is now an attribute of virtual servers.
Let say for instance you want to do cookie persistence on multiple virtual servers. You would create a "Persistence" profile with the specific attributes you need (in your case, cookie persistence). You can access these methods from the LocalLB::ProfilePersistence interface. Then for each virtual server, you would add the persistence profile that you created. This can be done with the LocalLB::VirtualServer::add_persistence_profile() method.
Just check out the following sections in the SDK and hopefully it will make sense.
LocalLB::PersistenceProfile
LocalLB::VirtualServer
Another way to get up to speed on these is to browse through the management GUI. The APIs follow the GUI fairly well.
-Joe