This script will report all VMs with a connected independent disc:
Just fill in the name of your vCenter Server name in the first line:
Connect-VIServer vcenter_server
$report = @()
Get-VM | where {$_ | Get-HardDisk | where {$_.Persistence -like "Independent*"}} | %{
$row = "" | Select VMname, HDname
$row.VMname = $_.Name
$row.HDname = ($_ | Get-HardDisk | where {$_.Persistence -like "Independent*"}).Name
$report += $row
}
$report