
Explanation/Reference:
Note:
* Manage search components in SharePoint Server 2013
Start a search service instance on a server
Retrieve the active search topology
Clone the active search topology
Add a search component
Remove a search component
Move a search component
Activate a search topology
* To make any changes to the search topology in a search installation that has items in the search index, you first have to create a new topology object. You modify this new topology object, a clone of the active topology, by adding or removing search components. After you have made the changes to the clone topology object, you make the clone the active topology.
* (incorrect)
You add an index replica to the search topology to achieve fault tolerance for an existing index partition.
Reference:https://technet.microsoft.com/en-us/library/jj862354.aspx