The amount of information logged and how long it is retained is controlled by the following NetBackup configuration parameters:
Vault logging level. Symantec recommends that you use a debug level of 5 when you generate logs that you send to Symantec for troubleshooting purposes. You can set the debug level to 5 for all Vault sessions or you can use the -verbose option on the vltrun command in the Vault policy that initiates the Vault job.
To set the duration and level for log files