create the symptom as you need it
If this is only for a specific group of VMs and the only different setting from the main policy then i would suggest that you create a new policy (as a sub policy) of the active one or create a new one of the base policy (depending on how you have the policies set up).
Create a custom group and assign the new policy to it and add the vms that you want the alert for to the group.
Again depending on how you have your policies you may need to disable you alert deff from other policies
under symptom deff filter for the name (in my case d:) and change the state as needed.
Again depending on your policies you may need to move the new one up the priority list for it to affect the objects.
The above is just for the c: and d: as this is the default that vrops will show. if the server has more disks than that click the gray box (select object) when creating the symptom deff and select a VM that has more than the default two disks. In my case it has an e:
