To work around the warning messages you have several options.
1. Increase the disk space to meet the NFA System Requirements.
2. Go to Administration->Watchdog Settings and set the "Disk Threshold" to over 95%, click save and recycle the "Netqos ReporterAnalyzer Watchdog Service".
3. You can change the freeSpacePercentage setting in the data_retention database by running:
update settings set value=20 where name='freeSpacePercentage';
Then recycle the CA NFA Data Retention Service
The example above would make sure the harvester does not go over 80% free space.