Cisco SD-WAN vSmart Controller

[RS19]

In my environment I have 2 vSmart Controllers.
Cisco is planning to have the maintenance of the vSmart controllers. 
They have planned for the maintenance 1 vSmart controller at a time ( 1 vSmart controller maintenance in 1 day & the 2nd vSmart controller in other day).

There will be reboot of the vSmart controllers during the maintenance. 
Cisco has mentioned that there will be interruption during this maintenance. 
Would like to understand why there will be interruption during this maintenance. I have 2 vSmart controllers. If 1 is rebooting there is 2nd vSmart controller & there should not be any impact.

Let me know will there be any impact in this scenario. When 2 vSmart controllers are there , my understanding is that there should not be any impact.

[Kanan Huseynli]

Run show omp peers on vSmart, between vSmarts there is OMP peering (routing peering).

[RS19]

Thanks. I checked it. Both the vSmarts vSmart-1 & vSmart-2 have OMP peering. 

[RS19]

So in my environment both the vSmart Controllers have the OMP peers established. Also the every cEdge have the OMP peer established with both the vSmart controllers.

Considering this my understanding along with the graceful restart timer, when Cisco performs the reboot or maintenace on 1 vSmart controller in separate days , there should not be any impact on my data plane communication.

Let me know if my understanding is right.

[Kanan Huseynli]

I've already explained the impact details. Please, re-read. Graceful restart has meaning when you don't have any active vSmart. But in your case, there will be active vSmart.