monthly retention

[Andrew Gideon]

On Sat, 04 Nov 2006 19:48:22 -0300, Manuel Kissoyan wrote:

> im trying to work out my backup with a monthly retention, wondering how i
> could keep a backup that is 30 days old all the time

You'll keep yourself confused as long as you word the problem that way. 
You [probably!] don't always want a backup that is 30 days old.  To do so
requires that you also have the 29 day old backup (for tomorrow) and the
28 day old backup (for the day after tomorrow) and ...

Well, you get the idea.

Reword the problem, and the solution becomes pretty obvious.  For example,
perhaps you want to save every 30th daily backup for 31 days.

You can also save yourself some mental effort by avoiding the phrase
"rotating". One rotates tapes.  Using a "to disk" tool like rsync for
backup (esp. given options like --link-dest {8^) eliminates that as a
consideration.

	- Andrew