To do this as a one-off just set up conditions like this:
Alert on a volume, set the conditions such that node
name is "yournode"
and Volume caption starts with "D:"
and (volumepercentused is greater than 90
volumefreespace is less than 100000000000)
Due to some quirks with the way the developers put together the volumes threshold tables you can't set a volume to alert when it crosses it's threshold through the UI so for a more scalable solution I use this custom SWQL alert, and it just alerts on any volume that is above it's threshold percentage, if no threshold has been set it uses the global defaults.
SELECT Volumes.Uri, Volumes.DisplayName FROM Orion.Volumes AS Volumes
join (SELECT v.volumeid
from orion.Volumes v
left join Orion.ForecastCapacitySettings fc on fc.InstanceId=v.VolumeID and fc.metricid=3
where v.volumepercentused >= case when fc.CriticalThreshold is null then (Select CurrentValue AS [col1] FROM Orion.Settings WHERE SettingID = 'NetPerfMon-DiskSpace-Error')
end) crit on volumes.volumeid=crit.volumeid
where volumes.volumetype like 'fixed%' or volumes.volumetype like '%network%' or volumes.volumetype like '%mount%'
I would use a Custom Property on the volume.
1. Create a Custom Property on Volumes for NumberOfAcceptableFreeBytes (or MB or % or as you like, you can use it for interface bandwidth too)
2. Stick a number in the Custom Property for your volume
3. In your Trigger conditions A) check whether there is a value & if there is a value
B) check the actual available free space
4. If the actual free space is smaller than the value in the Custom Property trigger an alert
This way you could set different limits on any volume you like without re-inventing the wheel each time.