The Operations Agent as it is currently designed is unable to send disk full alarms when the disk is 100% full on drive the agent is installed.
On startup, the agent should claim a minimal amount of space (temp file) that is required to send these alarms.
In our scenario, we alarm when the threshold is breached for a 15-minute period. The threshold was breached and went to 100% inside of 15 minutes. The problem had to be manually determined as the agent needs to be able to write to the disk to send the alarm.