Tape Rotations

In a tape rotation system, multiple tapes are organised into a tape backup pool, or tape backup library to provide you with data recovery capabilities, whilst allowing for selected backup tapes to be stored off-site for added security.

Different tapes are used for different days' backups according to a predefined system. Three such tape rotation systems are described here.

Five tape rotation - one per day

The simplest tape rotation scheme is to have one tape for each day of the working week. Tapes are labelled: Monday, Tuesday, Wednesday, Thursday, Friday.

For example, consider the calendar below:

Five tape rotation - one per day
Mon	Tue	Wed	Thurs	Fri
	1 Tues	2 Wed	3 Thurs	4 Fri
7 Mon	8 Tues	9 Wed	10 Thurs	11 Fri
14 Mon	15 Tues	16 Wed	17 Thurs	18 Fri
21 Mon	22 Tues	23 Wed	24 Thurs	25 Fri
28 Mon	29 Tues	30 Wed	31 Thurs

You can restore data from any one of the tapes in your library - or in this case, any day in the past the week. This strategy requires only five tapes, but only provides one week's data backup history.

Grandfather - Father - Son (GFS)

The grandfather - father - son schedule is the most widely used method, and involves backing up data in the following way:

• daily – on the “son tapes”
• weekly – on the “father tapes”
• monthly – on the “grandfather tapes”

This system is far more powerful than the five tape rotation, but requires more tapes.

For example, consider the calendar below:

Grandfather - Father - Son (GFS)
Mon	Tue	Wed	Thurs	Fri
	1 Tues	2 Wed	3 Thurs	4 Fri
7 Month1	8 Tues	9 Wed	10 Thurs	11 Fri
14 Week2	15 Tues	16 Wed	17 Thurs	18 Fri
21 Week3	22 Tues	23 Wed	24 Thurs	25 Fri
28 Week4	29 Tues	30 Wed	31 Thurs

This strategy provides you with the ability to restore data from the last week, plus any Monday over the last month, plus any month for as many monthly tapes as you have. Variations on this scheme are available, and provide a trade-off between the number of tapes required, and the number of monthly tapes available.