Compare hostnames and leases between CSV and DHCP info

Question

I have 3 nested loops and they do the following:

1. Get scopes from DHCP
2. Get hostnames from csv file
3. Compares hostnames and leases, matches are added to a hash table

There are 5 DHCP servers, 100's of scopes and thousands of leases.

What would be a good method to speed this up?

$DHServers = Get-DhcpServerInDC #get DHCP info
$hashtable = @{} #create hash table

foreach ($server in $DHServers){
$scopes = Get-DHCPServerv4Scope -ComputerName $server.dnsname #get all scopes in DHCP   
    
    foreach ($_ in (Import-Csv C:\script\Asset_List.csv | Select-Object -ExpandProperty asset)){ #get hostnames from list          
        
        foreach ($scope in $scopes){            
            if($scope | Get-DhcpServerV4Lease -ComputerName $server.dnsname | Where-Object HostName -like "$_*" ){ #compares the hostname to find which lease it is in
                $scopename=$scope.name #matches give scope name
                $hashtable[$_] = $scopename #when a match is found, add keys and values to table
            } 
        }
    }
}  
  
 

Answer 1

Piping the DHCP calls through foreach-object instead and then comparing at the end, cut the time down from 3min to 1min. Everything I have read made it seem like foreach was faster. Having DHCP being processed down the pipe with foreach-object instead of several iterations with foreach makes foreach-objects more efficient.

$servers = Get-DHCPServerInDC
$hashtable = @{}

# scopes into the leases to go into the PsCustomObject to be matched later
$leases = $servers | ForEach-Object {
    $server = $_.dnsname
    Get-DHCPServerv4Scope -computerName $server  #get scopes on DHCP serves
    
    } | ForEach-Object {
    $scope = $_
    $_ | Get-DHCPServerV4Lease -ComputerName $server | #get leases in all the scopes
    
     ForEach-Object {
        [pscustomobject]@{ # Make object to match later
        ScopeName = $scope.name #want name of scope only
        HostName  = $_.hostname #want hostname of leases
        }
    }
}



$assets = (Import-CSV c:\script\Asset_List.csv).asset #pull asset list
 
$assets | ForEach-Object { $asset = $_ #Go through hostnames finding matching lease

    $leases | Where-Object { #check leases
        $_.HostName -like "${asset}*" #find hostname 
    } | ForEach-Object {
        $hashtable[$asset] = $_.ScopeName #store matches
    }
}
```