Create a SharePoint 2013/2016 Search Topology on 4 nodes

CreateSearchServiceApplicationTopology.ps1

# Source https://technet.microsoft.com/en-us/library/jj862356.aspx

<# Specify the new servers you want to add search components to, start a search service instance (ssi) on these servers and 
create references to the search service instances #>

$hostA = Get-SPEnterpriseSearchServiceInstance -Identity "PRDS0270"
$hostB = Get-SPEnterpriseSearchServiceInstance -Identity "PRDS0271"
$hostC = Get-SPEnterpriseSearchServiceInstance -Identity "PRDS0272"
$hostD = Get-SPEnterpriseSearchServiceInstance -Identity "PRDS0273"

Start-SPEnterpriseSearchServiceInstance -Identity $hostA
Start-SPEnterpriseSearchServiceInstance -Identity $hostB
Start-SPEnterpriseSearchServiceInstance -Identity $hostC
Start-SPEnterpriseSearchServiceInstance -Identity $hostD

# Wait until all the search service instances are running

Get-SPEnterpriseSearchServiceInstance -Identity $hostA
Get-SPEnterpriseSearchServiceInstance -Identity $hostB
Get-SPEnterpriseSearchServiceInstance -Identity $hostC
Get-SPEnterpriseSearchServiceInstance -Identity $hostD

# Create a new search topology and a reference to the new search topology

$ssa = Get-SPEnterpriseSearchServiceApplication
$newTopology = New-SPEnterpriseSearchTopology -SearchApplication $ssa

<# Add all the search components to the new search topology. 
The following Windows PowerShell commands will create the search components of the new topology and assign them 
to the new servers. In this small enterprise search topology there is one index partition, index partition 0, 
to cater for a maximum of ten million items. This is indicated with the parameter -IndexPartition in the command 
New-SPEnterpriseSearchIndexComponent. The index partition has one index replica on virtual machine B and one index 
replica on virtual machine D. Each index replica will contain the exact same search index and is hosted on a 
different physical server to achieve fault tolerance. #>

New-SPEnterpriseSearchAdminComponent -SearchTopology $newTopology -SearchServiceInstance $hostA
New-SPEnterpriseSearchCrawlComponent -SearchTopology $newTopology -SearchServiceInstance $hostA
New-SPEnterpriseSearchContentProcessingComponent -SearchTopology $newTopology -SearchServiceInstance $hostA
New-SPEnterpriseSearchAnalyticsProcessingComponent -SearchTopology $newTopology -SearchServiceInstance $hostA
New-SPEnterpriseSearchQueryProcessingComponent -SearchTopology $newTopology -SearchServiceInstance $hostC
New-SPEnterpriseSearchIndexComponent -SearchTopology $newTopology -SearchServiceInstance $hostC -IndexPartition 0
New-SPEnterpriseSearchIndexComponent -SearchTopology $newTopology -SearchServiceInstance $hostC -IndexPartition 1

New-SPEnterpriseSearchAdminComponent -SearchTopology $newTopology -SearchServiceInstance $hostB
New-SPEnterpriseSearchCrawlComponent -SearchTopology $newTopology -SearchServiceInstance $hostB
New-SPEnterpriseSearchContentProcessingComponent -SearchTopology $newTopology -SearchServiceInstance $hostB
New-SPEnterpriseSearchAnalyticsProcessingComponent -SearchTopology $newTopology -SearchServiceInstance $hostB

New-SPEnterpriseSearchQueryProcessingComponent -SearchTopology $newTopology -SearchServiceInstance $hostD
New-SPEnterpriseSearchIndexComponent -SearchTopology $newTopology -SearchServiceInstance $hostD -IndexPartition 0 
New-SPEnterpriseSearchIndexComponent -SearchTopology $newTopology -SearchServiceInstance $hostD -IndexPartition 1

# Activate the new search topology

Set-SPEnterpriseSearchTopology -Identity $newTopology

# Verify that the new search topology is active

Get-SPEnterpriseSearchTopology -SearchApplication $ssa

# Verify that all components of the new search topology are running correctly.

Get-SPEnterpriseSearchStatus -SearchApplication $ssa -Text