Are you afraid of deleting old backups? I am. What if there’s something important in them, like files I deleted and didn’t realize I needed until months later?
Unfortunately, if you’re backing up regularly you’re going to run out of space eventually. At that point, you can either buy more space (more tapes, a new hard drive, etc.) or start deleting your old backups.
There is a solution, however.
It’s called GFS: Grandfather-father-son, a backup rotation scheme. The basic method is to define 3 backup sets, such as daily, weekly, and monthly. You could also choose daily, monthly, and yearly, if you really want to keep backups a long time.
Does it really make sense to keep 180 days worth of daily backups? Or would it make better sense to keep:
- 6 daily backups
- 4 weekly backups
- 12 monthly backups
That’s only 22 backups, yet it covers an entire year whereas our 180 daily backups only covers half a year. Pretty neat, huh? That’s GFS in a nutshell.
To use GFS with tape-based backup systems, simply rotate each of your daily, weekly, and monthly tapes according to their cycle. On the 7th day, the daily (son) graduates to a weekly backup (father). On the 4th week, the weekly backup graduates to a monthly (grandfather). The daily and weekly tapes get re-used during the cycle, while the monthly tapes are removed from the cycle and usually stored securely offsite.
What if I backup to a hard drive?
A GFS rotation scheme can be done in most modern-day backup software.
Create 3 separate jobs: one for daily, weekly, and monthly backups. Perform daily backups 6 days a week. On the 7th day, create a weekly backup. On the last day of the month, perform a monthly backup. Have the software keep no more than 6 versions of daily backups, keep 4 versions of weekly backups, and keep monthly backups as long as needed.