pool creation - on retention period

NBU 7.5.05

first time creating a pool. i came across the question of "retention period". if i select "infinity", would that mean:

1. once data has been deduplicated to one of the media in the pool, said media cannot be use to append more data OR
2. data can still be appended until the media is full but existing data will never be overwritten

regards,

rino