Reconfigure FAST for SharePoint 2010 server farm without resetting Index

       We recently expanded our FAST for SharePoint 2010 farm to include a second failover location. As it had been nearly a year since we rolled out our primary farm it was a good chance to validate our deployment documentation and to validate we could quickly and easily build our farm from scratch. All went well until the end in which we were validating the deployment of the FAST instance. It was discovered that the configuration of our FAST servers was incorrect. Unfortunately, this was discovered after we had spent several days completing the crawl of all our content. What the mistake was to assign the Query role to the wrong row of servers. Fortunately, it was possible to reconfigure the FAST servers without resetting or re-crawling our content by modifying the deployment.xml and running the Set-FASTSearchConfiguration PowerShell command. 

Environment detail:

• Windows 2008 R2 SP1 (KB976932)

• SharePoint 2010 SP1 w/June 2011 CU

• FAST for SharePoint 2010 SP1 w/June CU

§ 5 Rows

§ 4 Columns

Server role changes:

1. Remove the first row from serving queries.
2. Add the abilty for the second row to perform indexing.

Steps to Reconfigure:

1. Synchronize the primary and the backup indexer servers

https://technet.microsoft.com/en-us/library/gg482028.aspx

2. Reconfigure the farm deployment without adding new server.

https://technet.microsoft.com/en-us/library/ff381247.aspx#BKMK_ReconfigureTheDeploymentWithoutAddingNewServers