Optimize-DRSSeparateVMs.ps1

function Optimize-DRSSeparateVMs {
    <#
    .SYNOPSIS
    Creates DRS rules to keep similar VMs on separate VMHosts.Existing AntiAffinity rules are removed.
    If VMHosts.count is less than or equal to 4, the max VMs per group is count-1. Otherwise count-2
    .EXAMPLE
    Create DRS rules on MYCLUSTER
    Optimize-DRSSeparateVMs -Cluster MYCLUSTER
    .EXAMPLE
    Create DRS rules on all clusters
    Get-Cluster | Sort Name | %{ Optimize-DRSSeparateVMs -Cluster $_.Name }
    #>
    [cmdletbinding()]
    param (
        [Parameter(Mandatory=$true)]
        [string]$Cluster,
        [string]$ExclusionFilter = "*Veeam*"
    )

    try {
        $ErrorActionPreference = "STOP"
        # Get Cluster object
        $ClusterObj = Get-cluster -Name $Cluster

        # Remove existing VMAntiAffinity rules that dont match exclusion filter
        Get-Drsrule -Cluster $ClusterObj | Where-Object { $_.Name -notlike $ExclusionFilter -and $_.Type -eq "VMAntiAffinity" } | Remove-DrsRule -Confirm:$false

        # Get VMs in Cluster except for VMware DRS VMs and Veeam replicas
        $vms = $ClusterObj | get-vm | Sort-Object name | Where-Object { $_.name -notlike "*vcls*" -and $_.name -notlike "*replica*" }

        # Get VMHost in Cluster
        $vmhosts = @($ClusterObj | get-vmhost)
        if($vmhosts.count -le 4) {
            # Max VMs per group. Less than count to minimize issues with maintenance/failed VMHosts
            $max = $vmhosts.count - 1
        } else {
            $max = $vmhosts.count - 2
        }

        # Determine VM Type from characters 3-7 in VMName
        $vms | ForEach-Object { Add-Member -InputObject $_ -MemberType NoteProperty -Name Type -Value ($_.Name.Substring(3,4)) -Force }

        # Group VMs by Type. DRS groups are not needed with only 1 VM
        $groups = $vms | Group-Object -Property Type | Where-Object { $_.Count -gt 1 }

        # Split groups based on maximum of VMHosts-2 VMs per group
        $groups2 = foreach ($group in $groups) {
            Write-Host "Processing $($Group.Name)"
            # If group is greater than number of vmhosts then create multiple groups
            if ($group.count -gt $max) {
                # Counter for DRS rule index
                $index = 1
                for ($skip = 0; $skip -lt $group.group.count; $skip += $max) {
                    $members = $group.group | Select-Object -First $max -Skip $skip

                    if ($members.count -ne 1) {
                        [pscustomobject]@{
                            Count   = $vmhosts.count
                            Name    = $group.Name
                            Group   = $members
                            Counter = $index
                        }
                        $index++
                    }
                    else {
                        Write-Host "Only 1 member for $($group.Name + $index). No DRS rule needed"
                    }
                }
            }
            else {
                $group
            }
        }

        # Create DRS rules from groups
        foreach($group in $groups2) {
            if($null -ne $group.Counter) {
                $newName = "$($group.Name.ToUpper()) on Separate Hosts - $($group.Counter)"
            } else {
                $newName = "$($group.Name.ToUpper()) on Separate Hosts"
            }
            Write-Host "$($ClusterObj.Name)`: Creating $newName"
            New-DrsRule -Cluster $ClusterObj -Name "$newName" -KeepTogether:$false -VM $group.group
        }
    }
    catch {
        throw
    }
}