Backup: Media Sets

To be able to go back and recover data deleted some time ago (maybe days, maybe weeks),
you need to organize the backup-media (like tapes) in backup sets:

The principle is similar: one set of media for the daily backup, a second set for a larger
time span and maybe a third set for a very large time span :

Example 1: Monthly rotation on 2 sets ("Father - Son" method)

2 sets of backup media:

Set #1 (Blue):	31 media , labeled "Day 1" to Day 31", used every day on Monday to Friday except on the first workday of a month, when a media of the set#2 is used. reused after 1 month (if a day is on a weekend or holiday, then that media is skipped)
Set #2 (Red):	typically 12 media, labeled "Jan", "Feb",...."Dec". Used on the first workday of a month ( instead of the media of the set#1 )

Example 2: Weekly rotation on 3 sets ("Grandfather - Father - Son" method)

3 sets of backup media:

Set #1 (Blue)	4 media, labeled "Monday", Tuesday","Wednesday", Thursday" reused after 1 week
Set #2 (Red)	4 media, labeled "week 2","week 3","week 3","week 4", used on each Friday (except on first Friday of a month, when media of set#3 is used ) reused after 1 month
Set #3 (Green)	typically 12 media, labeled "Jan", "Feb",...."Dec". Used on the first Friday of a month ( instead of the media of the set#2 )

Both above examples allow you to go back for 12 months to retrieve data from Backup-tapes.
(and I know some companies, where the media of the Monthly-Set are NEVER reused,
a new media is used each months, allowing them to go back for YEARS ! )

Before you ask the question: "My media has a very high capacity, I could append multiple days
on one media to save some money"
Don't ! My experience: keep the backup procedure as simple as possible, appending data to
other backups will only cause confusion.
And when using tapes: DON'T ! because appending will require to wind forward the tapes
each time, shortening their life-time much quicker than using one tape per day.

However, you can save some time using different backup methods.