GTM load balancing between to DC's?

Hi

We have DC & DR site in our network currently we are using GTM by sending request only to DC side we want a mechanism to send few request DR site as well We want to do this to check so that we have confirmation that DR site is also available every time and in sync.

Query is:

We need to set the priority where F5 should resolve 99 times DC requests and 1 time DR should be resolved ,For instance if there are 100 DNS query requests for a.xyz.ac , 99 requests should be served by DC and 1 request should be served by DR servers(this is applicable for both intranet and internet request).