The firewall automatically deletes logs that exceed the expiration period. When the firewall reaches the storage quota for a log type, it automatically deletes older logs of that type to create space even if you don’t set an expiration period.
If you want to manually delete logs, select Device > Log Settings and, in the Manage Logs section, click the links to clear logs by type.
Configure Log Storage Quotas and Expiration Periods
Select Device > Setup > Management and edit the Logging and Reporting Settings.
Select Log Storage and enter a Quota (%) for each log type. When you change a percentage value, the dialog refreshes to display the corresponding absolute value (Quota GB/MB column).
Enter the Max Days (expiration period) for each log type (range is 1-2,000). The fields are blank by default, which means the logs never expire. The firewall synchronizes expiration periods across high availability (HA) pairs. Because only the active HA peer generates logs, the passive peer has no logs to delete unless failover occurs and it starts generating logs.
Click OK and Commit.

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