From our VI Toolkit snippet-vault.

The following 2 functions do probably most of what you want.

Function add-HD uses an existing .vmdk file to create a hard disk on a VM.

The calling syntax: add-HD <VM-name> <datastore-name> <path-to-vmdk> <controller-label>

An example: add-HD "PC4" "vmfs2" "PC4/PC4.vmdk" "SCSI Controller 0"

Function remove-HD removes a hard disk from a VM and optionally deletes the .vmdk file.

The calling syntax: remove-HD <VM-name> <hard-disk-label> <delete-flag>

An example: remove-HD "PC4" "Hard Disk 3" $TRUE

The code:

Get-VIServer -Server <VC-server>

[http://Reflection.Assembly|http://Reflection.Assembly]::LoadWithPartialName("vmware.vim")

function remove-HD {
  param($VMname, $HDname, $Delflag)
  
  $vm = Get-View (Get-VM $VMname).ID

  foreach($dev in $vm.Config.Hardware.Device){
    if ($dev.DeviceInfo.Label -eq $HDname){
      $key = $dev.Key
       $name = $dev.Backing.FileName
    }
  }

  $spec = New-Object VMware.Vim.VirtualMachineConfigSpec
  $spec.deviceChange = @()
  $spec.deviceChange += New-Object VMware.Vim.VirtualDeviceConfigSpec
  $spec.deviceChange[0].device = New-Object VMware.Vim.VirtualDevice
  $spec.deviceChange[0].device.key = $key
  $spec.deviceChange[0].operation = "remove"

  $vm.ReconfigVM_Task($spec)

  if ($Delflag){
    $svcRef = new-object VMware.Vim.ManagedObjectReference
    $svcRef.Type = "ServiceInstance"
    $svcRef.Value = "ServiceInstance"
    $serviceInstance = get-view $svcRef

    $fileMgr = Get-View $serviceInstance.Content.fileManager

    $datacenter = (Get-View (Get-VM $VMname | Get-Datacenter).ID).get_MoRef()
     
    $fileMgr.DeleteDatastoreFile_Task($name, $datacenter)
  }
}

function add-HD {
  param($VMname, $DSname, $Filename, $SCSIcntrl)

  $vm = Get-View (Get-VM $VMname).ID
  $ds = Get-View (Get-Datastore -Name $DSname).ID
  foreach($dev in $vm.config.hardware.device){
    if ($dev.deviceInfo.label -eq $SCSIcntrl){
       $CntrlKey = $dev.key
     }
  }
  $Unitnumber = 0
  $DevKey = 0
  foreach($dev in $vm.config.hardware.device){
    if ($dev.controllerKey -eq $CntrlKey){
       if ($dev.Unitnumber -gt $Unitnumber){$Unitnumber = $dev.Unitnumber}
       if ($dev.key -gt $DevKey) {$DevKey = $dev.key}
     }
  }

  $spec = New-Object VMware.Vim.VirtualMachineConfigSpec
  $spec.deviceChange = @()
  $spec.deviceChange += New-Object VMware.Vim.VirtualDeviceConfigSpec

  $spec.deviceChange[0].device = New-Object VMware.Vim.VirtualDisk
  $spec.deviceChange[0].device.backing = New-Object VMware.Vim.VirtualDiskFlatVer2BackingInfo
  $spec.deviceChange[0].device.backing.datastore = $ds.MoRef
  $spec.deviceChange[0].device.backing.fileName = "[" + $DSname + "] " + $Filename
  $spec.deviceChange[0].device.backing.diskMode = "independent_persistent"
  $spec.deviceChange[0].device.key = $DevKey + 1
  $spec.deviceChange[0].device.unitnumber = $Unitnumber + 1
  $spec.deviceChange[0].device.controllerKey = $CntrlKey
  $spec.deviceChange[0].operation = "add"

  $vm.ReconfigVM_Task($spec)
}

Since the forum SW apparently has a mind of it's own I have attached the code.

Note that the functions can definitely be improved.

Currently the fail-safe mechanisms are quit limited.

If there is a need to explain parts of the code please let me know.

And of course, use in a production environment at your own risk !