Hi, speaking about ArubaOS-Switch based switch series - such as Aruba 5400R zl2 and Aruba 2930F - the VSF (Virtual Switching Framework) implementation does not require any licensing, it's a feature contained in the recent/current AOS-Switch software main releases (say it was introduced with AOS-Switch 16.02 main software release on Aruba 5400R zl2 Switch series).
Specifically speaking about Aruba 5400R zl2 series (not to be confused with HP 5400zl Switch series) there is enough documentation to understand requirements and properties (say as example
this quite old technical whitepaper or
this presentation).
Basically to form a VSF prerequisites require that you have two Aruba 5406R zl2 or two Aruba 5412R zl2 (you can't mix say an Aruba 5406R zl2 with an Aruba 5412R zl2 together) operating in v3 only mode and so with only v3 zl2 Modules (differences between other generations and the latest v3 zl3 are explained
here, and v3 zl2 Modules installation guide
here). You also need 10G or 40G VSF Links (generally made with DAC) and then it's a matter of software configuration. Keep in mind that each VSF Member will work with just one Management Module (the other is taken offline if installed <- no redundancy at chassis level as when you deal with two MMs on a single standalone Chassis).
Consider to read also the VSF dedicated Chapter on the official Aruba 3810M/5400R zl2 Management and Configuration Guide (for ArubaOS-Switch 16.10) available
here (docs can be freely and easily browsed on asp.arubanetworks.com portal).