Re: It is not just about numbers here
"Old backups can be vital."
Here's an example: In 1999 a NEAX61M switch was rebooted to allow y2k updates to take effect.
It failed at reboot, and the failure cascaded to 3 other switches, putting 200,000 phone lines out of action as well as a major international switch, resulting in subscribers throughout the country being unable to make long distance and international calls.
BACKUPS WERE CORRUPT. It turned out that something had scribbled over memory more than a year previously and what was backed up was copletely corrupt information.
Techs had to go back more than 2 years before they found a working backup - that was ok, the switch booted up - BUT 2 years means a LOT of changes around (people move houeses, etc etc etc), so the next step was to replay all database changes - which thankfully had been backed up separately.
It took more than a DAY before anyone could make any phone calls at all in Palmerston North - but there were still thousands of people who found they couldn't make calls.
It took 6 _WEEKS_ to replay those database updates. In that period various people had no dial tone, the wrong number, etc etc etc. A small ISP had more than half its lines out of action for most of that period.
Lesson1: Older backups can be vital
Lesson2: A backup is no fucking good if it hasn't been tested.
240 copies of small pieces of data such as mail folders is immaterial. 240 copies of a 1Tb filesystem is another matter.
I admin backups for about 1Pb of data. It's all about mintaining a balance between COSTS (and frankly tapes are the cheapest part of the whole shebang, so I don't really care if I use a bunch of extra LTO5s at 14 quid a pop), resiliance,complying with data retention laws, keeping archival copes and being able to run the backups in a reasonable time window. (Some areas are backed up 7-10 times per day, others are only touched once a week.)
A good backup system has a backing database so an admin can zero in on a given file at a given point in time in 2-3 minutes. That database is also a BRILLIANT intrusion/modification detection system - if any aspect of a file changes, its SHA512 signature changes and that means it gets backed up again.
It can tell you how many copies of any given file are backed up.
It also doesn't miss things if a file tree is moved - the number of backup systems which will detect and handle this correctly can be counted on one hand - 2 are free and the other 2 cost in excess of £30k.
The vast majority of "backup" systems out there are crap - and the ones being most heavily promoted commercially certainly fall into that camp.