I to create an alert that tells me when I have less than 10 GB free on the \ of a guest VM. I have only found alerts for percentage of free space, but not actual data size
Have you tried using this variable? ${N=SwisEntity;M=VolumeSpaceAvailableExp}
We use this in our alerts and for our needs it works great in giving us an actual amount along with the percentage as well. This way we have any entire picture of disk space for the specific device monitored.