We have over 500 iPads and 100 Apple TV's on one site. We are having issues with iOS8 trying to AirPlay to the Apple TV's as the list is to large. We have a SSID specifically for iPads & ATV's across the site and want to VLAN by building throughout the site to reduce the list. Our problems are that the buildings are within close proximity and want to make sure our devices when roaming around the site between buildings get the correct IP within a VLAN. (we are using iPad 2's). iPad users work across the whole site every hour.
Yes, you do need VLAN segmentation to reduce your broadcast domains and per building is a good start. It doesn't make sense to have more ATVs than clients can see/list.
I understand too, having building WLAN Groups that use VLAN-override to assign VLAN to SSIDs, your clients would be ok if they lose connection walking between buildings, as they would DHCP on the new building VLAN when they reconnect.
But, if they do remain associated going between building/AP groups, they would have/use their old VLAN IPs until they do a release/renew or purposely re-connect. You might use a short lease time or need to use different building SSIDs if the overlap is too much.
If you have many individual buildings on individual VLANs, you might use Bonjour Gateway to permit ATV between the next to one another neighbor building VLANs as another alternative, so the users would be ok until they re-DHCP.
Would there be much of a delay as a client moves from one building vlan to another, when they are using the same SSID via vlan overides? My worry is that the Ipad 2 running ios7 and 8 will not realise that the vlan has changed, especially if they moved between the reaches of 5 building vlans in the space of 60 seconds using the same SSID. Would this require creating more building SSIDs as I think that changing the DHCP lease on a Windows 2008 server time to 60 seconds might put a lot of load on the system and the clients? Would using Radius be of any benefit to our situation, as we want to later link authentication for byod devices with a lightspeed transparent proxy hosted by our ISP, so they only have to sign on once.