Here is a good link:
http://www.cisco.com/en/US/docs/wireless/technology/controller/deployment/guide/dep.html#wp1050985
from the url above:
Another deployment strategy is to use the "Master Controller" option during the deployment phase. The idea is to have access points join a Master Controller as they are deployed and then have the administrator assign them a primary, secondary, and/or tertiary controller. This is also a good time to place the access points on WCS maps. Here are the basic recommendations for using the Master Controller option:
1. Deploy the WLCs in the network.
2. Create the mobility group for the WLCs and assign the controllers to the same mobility group (see the Advanced Deployment section for further help on this).
3. Select one of the WLCs to be the Master Controller and turn Master Controller Mode on for that controller. To turn Master Controller Mode on, login to the WLC and navigate to Controller | Master Controller Mode. Check the "Master Controller Mode" box and then click on the Apply button. Figure 5 shows the Master Controller Mode interface:
4. Implement a strategy to have the access points learn the Master Controller IP address during the LWAPP Discovery process. For example, configure the Master Controller's Management Interface IP address in the vendor specific Option 43 in the DHCP server.
5. Proceed with deploying the access points. Assuming that the access points have not previously been configured with a primary, secondary, and/or tertiary controller, the access points should join the Master Controller.
6. You may now assign these joined access points to the desired primary, secondary, and/or tertiary WLCs (see the Advanced Deployment section). This is also a good time to place the access points in maps in the WCS.
7. After completing your access point deployment, Cisco recommends that you turn Master Controller Mode off.
8. See # 7
