Re: Total Storage amount in datacenter

You could try something like this

Get-Datacenter|SelectName,
@{N="Storage Used (GB)";E={
  $sum=Get-Datastore-Location$_|
  where {$_.ExtensionData.Summary.MultipleHostAccess-and$_.Type-eq"VMFS"} |
  Measure-Object-PropertyCapacityGB,FreeSpaceGB-Sum
  [Math]::Round($sum[0].Sum-$sum[1].Sum,2)
}}

It will only take shared VMFS datastores into account.

If you use other datastore types you can change the Where-clause