Environment : This KB is applicable to all the versions of clearpass.
Clearpass runs multiple clean up scripts every night.
One of the major clean up scripts is the SystemCleanup which is run using a cronjob at 02:45 am every night.
After reducing the retention settings you can expect clearpass to clean up the disk space at night. This also depends on the reduction of the number of days.
In case you see any disk space warnings in the event viewer. You have to reduce the retention settings and run this script manually to clean up.
Please call Aruba TAC in case you need to run the script manually.