The only way to get continuous availability for SMB and Isilon is if the following conditions are met:  1. Client is using SMB3 (min Win8 or Server 2012R2) 2. Cluster is at least OneFS 8.0 (currently, not as an upgrade target) 3. The SMB share has CA enabled  If any of these conditions are not met, then SMB clients will disconnect if the node to which it is connected goes away.  The client will then have to reconnect.  This reconnection can be done immediately as the client will ask DNS for a new IP address and will get another IP on another node.  For most users this isn't a big deal.  They get disconnected and try again and reconnect.  For applications, this can be more problematic, the severity will depend on how the application behaves when the SMB session is disconnected.  Most do not handle this gracefully, in my experience.
Would the windows 7 clients running smb 2 get disconnected during one fs 7.2 node upgrades ? The clients that have connection to any node that gets upgraded and rebooted would get disconnected ? My understanding for continuous client availability during node reboots if they need to be on smb3 or windows 8 or windows 10 ? is this true ? 
Isilon one fs 7.2 upgrade and SMB 2 client connection availability.