Exclude UBS drives from query results for Percentage FreeSpace

RCDevops777 

I suspect you'll need another source of data as well as the Perf table.  Ideas could be, a custom log (using PowerShell / Logic Apps, one example of this) to find this data and upload that to Log analytics, or enable auditing

However note, auditing would only have data (event id 4663) for new drives added.  

if you are lucky to have USB drives of a certain size then maybe exclude those?

Note: you need the extra Perf counter "Free Megabytes"

//
// combine % free and Free space to get volume size as well as %free
//

Perf
//| where Computer startswith "RDS" 
| where CounterName == "Free Megabytes"
| where TimeGenerated > startofday(ago(1d))
| where InstanceName has ":" and strlen(InstanceName) ==2 // only look at drive letters
| summarize MbFree=avg(CounterValue) by Computer,InstanceName,bin(TimeGenerated, 5m)
| summarize arg_max(TimeGenerated, *) by Computer,InstanceName
|join kind= inner
(
    Perf
    | where CounterName == "% Free Space"
    | where TimeGenerated > startofday(ago(1d))
    | where InstanceName has ":" and strlen(InstanceName) ==2 // only look at drives with letters
    | summarize PctFree=avg(CounterValue) by Computer,InstanceName,bin(TimeGenerated, 5m)
    | summarize arg_max(TimeGenerated, *) by Computer,InstanceName
)
on Computer , InstanceName 
| project   TotalSizeGB=round(MbFree*100/PctFree/1024,0), 
            round(PctFree,2),
            round(MbFree,2), 
            Computer, 
            InstanceName
| summarize FreePCT=avg(PctFree) by Computer,
            DriveLetter = InstanceName,
            TotalSizeGB,
            FreeGB = round(MbFree / 1024,2)
| sort by DriveLetter  asc

Example PowerShell: https://devblogs.microsoft.com/scripting/inventory-drive-types-by-using-powershell/ and https://docs.microsoft.com/en-us/azure/azure-monitor/platform/runbook-datacollect