Example--Daily Cumulative, Weekly Cumulative Backups

Table 33-7 shows the most commonly used incremental backup schedule; it is recommended for most situations. With this schedule:

• All files that have changed since the lower-level backup at the end of the previous week are saved each day.

• For each weekday level 9 backup, the previous level 0 or level 5 is the closest backup at a lower level. Therefore, each weekday tape contains all the files changed since the end of the previous week (or the initial level 0 for the first week).

• For each Friday level 5 backup, the nearest lower-level backup is the level 0 done at the beginning of the month. Therefore, each Friday's tape contains all the files changed during the month to that point.

Table 33-7 Daily Cumulative/Weekly Cumulative Backup Schedule

	Floating	Mon	Tues	Wed	Thurs	Fri
1st of Month	0
Week 1		9	9	9	9	5
Week 2		9	9	9	9	5
Week 3		9	9	9	9	5
Week 4		9	9	9	9	5

Table 33-8 shows how the contents of the tapes can change across two weeks using the previous schedule. Each letter represents a different file.

Table 33-8 Contents of Tapes for Daily/Weekly Cumulative Schedule

	Mon	Tues	Wed	Thurs	Fri
Week 1	a b	a b c	a b c d	a b c d e	a b c d e f
Week 2	g	g h	g h i	g h i j	a b c d e f g h i j k

Tape Needs

With this schedule, you will need six tapes (if you want to reuse daily tapes), or nine tapes (if you want to use four different daily tapes): one for the level 0, four for the Fridays, and one or four daily tapes.

If you need to restore a complete file system, you will need the following tapes: the level 0, the most recent Friday tape, and the most recent daily tape since the last Friday tape (if any).