Function Get-DrsGroup {
<#
.SYNOPSIS
Retrieves DRS groups from a cluster.

.DESCRIPTION
Retrieves DRS groups from a cluster.

.PARAMETER Cluster
Specify the cluster for which you want to retrieve the DRS groups

.PARAMETER Name
Specify the name of the DRS group you want to retrieve.

.EXAMPLE
Get-DrsGroup -Cluster $Cluster -Name "VMs DRS Group"
Retrieves the DRS group "Vms DRS Group" from cluster $Cluster.

.EXAMPLE
Get-Cluster | Get-DrsGroup
Retrieves all the DRS groups for all clusters.

.INPUTS
ClusterImpl

.OUTPUTS
ClusterVmGroup
ClusterHostGroup

.COMPONENT
VMware vSphere PowerCLI
#>

  param([parameter(Mandatory=$true, ValueFromPipeline=$true)]$Cluster,
        [string] $Name="*")

  process {
    $Cluster = Get-Cluster -Name $Cluster
    if($Cluster) {
      $Cluster.ExtensionData.ConfigurationEx.Group | `
      Where-Object {$_.Name -like $Name}
    }
  }
}
  
Function Add-VMToDrsGroup {
<#
.SYNOPSIS
Adds a virtual machine to a cluster VM DRS group.

.DESCRIPTION
Adds a virtual machine to a cluster VM DRS group.

.PARAMETER Cluster
Specify the cluster for which you want to retrieve the DRS groups

.PARAMETER DrsGroup
Specify the DRS group you want to retrieve.

.PARAMETER VM
Specify the virtual machine you want to add to the DRS Group.

.EXAMPLE
Add-VMToDrsGroup -Cluster $Cluster -DrsGroup "VM DRS Group" -VM $VM
Adds virtual machine $VM to the DRS group "VM DRS Group" of cluster $Cluster.

.EXAMPLE
Get-Cluster MyCluster | Get-VM "A*" | Add-VMToDrsGroup -Cluster MyCluster -DrsGroup $DrsGroup
Adds all virtual machines with a name starting with "A" in cluster MyCluster to the DRS group $DrsGroup of cluster MyCluster.

.INPUTS
VirtualMachineImpl

.OUTPUTS
Task

.COMPONENT
VMware vSphere PowerCLI
#>

  param([parameter(Mandatory=$true)] $Cluster,
        [parameter(Mandatory=$true)] $DrsGroup,
        [parameter(Mandatory=$true, ValueFromPipeline=$true)] $VM)
        
  begin {
    $Cluster = Get-Cluster -Name $Cluster
  }
  
  process {
    if ($Cluster) {
      if ($DrsGroup.GetType().Name -eq "string") {
        $DrsGroupName = $DrsGroup
        $DrsGroup = Get-DrsGroup -Cluster $Cluster -Name $DrsGroup
      }
      if (-not $DrsGroup) {
        Write-Error "The DrsGroup $DrsGroupName was not found on cluster $($Cluster.name)."
      }
      else { 
        if ($DrsGroup.GetType().Name -ne "ClusterVmGroup") {
          Write-Error "The DrsGroup $DrsGroupName on cluster $($Cluster.Name) doesn't have the required type ClusterVmGroup."
        }
        else {
          $VM = $Cluster | Get-VM -Name $VM
          If ($VM) {
            $spec = New-Object VMware.Vim.ClusterConfigSpecEx
            $spec.groupSpec = New-Object VMware.Vim.ClusterGroupSpec[] (1)
            $spec.groupSpec[0] = New-Object VMware.Vim.ClusterGroupSpec
            $spec.groupSpec[0].operation = "edit"
            $spec.groupSpec[0].info = $DrsGroup
            $spec.groupSpec[0].info.vm += $VM.ExtensionData.MoRef

            $Cluster.ExtensionData.ReconfigureComputeResource_Task($spec, $true)
          }
        }
      }
    }
  }
}