How can I alert on down disk volume but not because of node SNMP lost?
Once upon a time :), there was an option to alert on down disk, but there is no more 'down' status for a disk.
When looking at the 'Volumes' table, there is no down status (status=2) for a volume that not exist on the node anymore.
When a disk disappeared (label changed, Hard drive cut off, etc.) his status changes to 0 (unknown) like disks of nodes that lost SNMP.