Okay, so we have 3.5.1. All of our APs are in the same zone. The majority of our APs are zf7372. If we upgrade to 3.6.2. I know the 7372 APs will still work. If we then upgrade to 5.0 or 5.1, the firmware from 3.6.2 will remain on the controller.
From what I'm understanding we can keep all our APs, including the zf7372 model, running 3.6.2 in the same zone. If we want to upgrade the firmware on APs that support the higher firmware, like the R700 and R710, we can create a new zone that has firmware version 5.0 or 5.1.
If we can indeed continue to run the 7372s on 5.1 using the old firmware, are there any drawbacks, performance or otherwise to doing this rather than remaining on 3.6.2?
As long as your 7372 AP's are in an existing AP zone running 3.6.2 firmware you should be able to upgrade the cluster to 5.1 (follow upgrade path in release notes) and create new AP zones with 5.1 code to support new AP models.
You will not be able to create new AP zones with 3.6.2 firmware after upgrading to 5.1 - so make sure they exist before you upgrade (maybe make a spare!!)
You will not be able to upgrade to 5.2 or higher level code as the policy is to support n-2 AP versions (3.6.2, 5.0, 5.1 major versions that can coexist on 5.1)