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#----------------------------------------------------------------------------- 
# Name:               Move-SPEnterpriseSearchIndex.ps1  
# Description:         This script will move the SharePoint 2013 Search Index 
#                     
# Usage:            Run the function with the 3 required Parameters 
# By:                 Ivan Josipovic, Softlanding.ca  
#----------------------------------------------------------------------------- 
function Move-SPEnterpriseSearchIndex($SearchServiceName,$Server,$IndexLocation){ 
    Add-PSSnapin Microsoft.SharePoint.PowerShell -ea 0; 
    #Gets the Search Service Application 
    $SSA = Get-SPServiceApplication -Name $SearchServiceName; 
    if (!$?){throw "Cant find a Search Service Application: `"$SearchServiceName`"";} 
    #Gets the Search Service Instance on the Specified Server 
    $Instance = Get-SPEnterpriseSearchServiceInstance -Identity $Server; 
    if (!$?){throw "Cant find a Search Service Instance on Server: `"$Server`"";} 
    #Gets the current Search Topology 
    $Current = Get-SPEnterpriseSearchTopology -SearchApplication $SSA -Active; 
    if (!$?){throw "There is no Active Topology, you can try removing the `"-Active`" from the line above in the script";} 
    #Creates a Copy of the current Search Topology 
    $Clone = New-SPEnterpriseSearchTopology -Clone -SearchApplication $SSA -SearchTopology $Current; 
    #Adds a new Index Component with the new Index Location 
    New-SPEnterpriseSearchIndexComponent -SearchTopology $Clone -IndexPartition 0 -SearchServiceInstance $Instance -RootDirectory $IndexLocation | Out-Null; 
    if (!$?){throw "Make sure that Index Location `"$IndexLocation`" exists on Server: `"$Server`"";} 
    #Sets our new Search Topology as Active 
    Set-SPEnterpriseSearchTopology -Identity $Clone; 
    #Removes the old Search Topology 
    Remove-SPEnterpriseSearchTopology -Identity $Current -Confirm:$false; 
    #Now we need to remove the extra Index Component 
    #Gets the Search Topology 
    $Current = Get-SPEnterpriseSearchTopology -SearchApplication $SSA -Active; 
    #Creates a copy of the current Search Topology 
    $Clone=New-SPEnterpriseSearchTopology -Clone -SearchApplication $SSA -SearchTopology $Current; 
    #Removes the old Index Component from the Search Topology 
    Get-SPEnterpriseSearchComponent -SearchTopology $Clone | ? {($_.GetType().Name -eq "IndexComponent"-and ($_.ServerName -eq $($Instance.Server.Address)) -and ($_.RootDirectory -ne $IndexLocation)} | Remove-SPEnterpriseSearchComponent -SearchTopology $Clone -Confirm:$false; 
    #Sets our new Search Topology as Active 
    Set-SPEnterpriseSearchTopology -Identity $Clone; 
    #Removes the old Search Topology 
    Remove-SPEnterpriseSearchTopology -Identity $Current -Confirm:$False; 
    Write-Host "The Index has been moved to $IndexLocation on $Server" 
    Write-Host "This will not remove the data from the old index location. You will have to do that manually :)" 
} 
 
Move-SPEnterpriseSearchIndex -SearchServiceName "Search Service Application" -Server "SP2013-WFE" -IndexLocation "C:\Index"
 SharePoint 2013 places the Search index in the C: by default. There are many reasons why you would want to move the index to a different places.
This script will take three parameters, the Search Service Name, the Server Name and Index Location.  There is an example on the bottom of the script.
More info on my blog: http://www.softlanding.ca/Blog/default.aspx