Topic Last Modified: 2011-03-02

To failback and resume normal operation at the North site, the following steps are necessary:

1. Restore network connection between two sites. Quality attributes of the network connection (for example, bandwidth, latency, and loss) should be comparable to the quality prior to failover.
   
   
2. Ensure that geographically redundant hardware load balancers at the South site can communicate with their redundant counterparts at the North site. Also, ensure that the hardware load balancers at the North site resume their normal operation.
   
   
3. Resynchronize storage so data in North is in full sync with data in South.
   
   
4. Bring online all servers and relevant infrastructure in North. Depending on the severity of the North site’s failure, it might be necessary to build everything from scratch. On the other hand, if North had suffered from, say, an extended power failure, all equipment would probably come online automatically (or at least under managed supervision).
   
   Note that if a Front End Server comes back up before the DNS server and domain controllers are up, it may fail to start. You can then manually start it after the DNS server and domain controllers are running.
   
   
5. If many or all of the servers in the North site were down, bring them back up in the following order:
   
   
   • Start the DNS servers and domain controllers.
     
     
   • Verify that the firewalls are up.
     
     
   • Start the Edge Servers.
     
     
   • Start the SQL Servers.
     
     
   • Start the Archiving Server and Monitoring Server.
     
     
   • Start the Director pool.
     
     
   • Start the A/V Conferencing pool.
     
     
   • Start the Exchange Servers.
     
     
   • Finally, start the Front End Servers.
     
     
6. After you have started the SQL Servers in the previous step, you can fail back the server clusters from South to North so that cluster resources are owned by servers at the North site. Only at this point might users be affected. If they try to do something new, such as publish presence or schedule a conference, the operation will fail for the duration of the failback, but users should remain logged on.