NetWorker maintains an index which contains the details of each backed up file (name, location, access credential, file size, backup date, owner ship ...). This index is the so called CFI (client file index). Depending on the amount of saved files per backup cycle and the amount of backup cycles the CFI can grow huge.
NetWorker has two different clean up policies: One for the backups on the backup media (retention policy) and one to clean up (maintain) the CFI (browse policy).
If the retention policy is exceeded, the file is deleted (or marked NetWorker internal as deletable), if the browse policy is exceeded the CFI is clean up.
If e. g. the browse policy was set to 1 month and retention policy to 2 month the backup is kept at least two moth on the backup media. After one month the CFI is cleaned up.
If you want to recover a backup which is older than 1 month (but younger than 2 month) you're not able to query the CFI for the file. You've two options for the recovery:
Browse Policy defines the lifecycle of the file index data for the save set
Retention Policy defines the lifecycle of the save set itself (how long it remains recoverable).
Until NW 8, the retention policy can be longer than the browse policy.
Since NW 9 the browse policy is gone (BP and RP have the same value).
Especially for disk backup devices you must just ensure that you have enough space to keep the save sets for one more month.
your statement is a bit fuzzy - please let me clarify some tiny details.
"If the retention policy is exceeded, the file ..." - when the backup is inserted into the media database, the relative policy
will be converted into an absolute date. Consequently, not the policy but only date can be passed.
Not the 'file' will be deleted but the save set (as long as it is stored on a disk media).
"cleaning up the CFI" means "if it exists, the CFI for this save set will be deleted".
In fact you've 3 options for the recovery: