Generally user data deletion happens in multiple phases for large companies that care about both compliance and user experience.
For example, if you delete an email or document on Google it moves to the "Trash" folder for 30 days.
When you manually empty the trash or the time window expires, most likely the next step would be a soft deletion for a few days where the data is still on hard drives but hidden from the application. Soft deletion is mainly protection against coding errors, since soft deletion is easy to undo if you've caused an incident but hard deletion (removing the data from disk) is not.
Then most likely a garbage collection process comes by a few days later and hard deletes the data from disk, leaving it only on tape backups
Finally, maybe a month or two later it disappears from the tape backups as they get rotated or otherwise disposed of
This addresses the needs of:
- Giving a good user experience (user "oops I made a mistake" undelete)
- Protecting against incidents due to coding errors (software engineer "oops I made a mistake" undelete)
- Making sure data disappears from both disk and backups within a certain time window, like maybe 30 or 60 days (comply with regulation and user expectations of data being cleared)