Hi Julian,
I understand you are going to deploy 5406z and want redundancy.
The need of the "Redundancy" is defined well with below points:
- How important that network segment is to the network
- Number of user/Access Layer devices that might get affected
- How strong the technical team is presented in the location to recover the network incase of outage
- The End Customers budget concern
- There are other few questions that you might ask related to the case
In 5406R, you can have Redundant Management module (2nd J9827A) to have the module failure redundancy.(If budgetary becomes a concern over other questions above)
If you are looking for chassis redundancy, (assuming the aforesaid question have answers as Yes/Critical as answers) we can go ahead and propose 2unitsx 5406R
As of last time I checked, the Standby depoyment should be replica of the Commander Switch.
Hope the VSF document Link and the community link might help you.