PS Get used space on all volumes

gwmi win32_volume -Filter ‘drivetype = 3’ | select driveletter, label, @{LABEL=’GBcapacity’;EXPRESSION={$_.capacity/1GB} }, @{LABEL=’GBfreespace’;EXPRESSION={$_.freespace/1GB} }

Reset VSS Writer status

Get VSS writers:
vssadmin list writers

To reset VSS Writer status from Retryable or Non-retryable error you need to restart Hyper-V Virtual Machine Management service. Service restart does not affect VM only your ability to manage VM  through Hyper-V Manager console.

Source: social.technet.microsoft.com