API call to get space usage details

Hi, can anyone suggest what the correct API call is to get details on total space and consumed space on the Unity?

I've read the documentation and programming guide but I just can't figure it out.  I've tried variations on the following with no joy.

https://unityHostname/api/types/metric/?filter=path lk sp.*.storage.%25

I can collect other metrics successfully, for example,

https://unityHostname/api/types/metricValue/instances?filter=path EQ "sp.*.cpu.summary.utilization"

thanks!