Table 23–7 shows the most commonly used incremental backup schedule. This schedule is recommended for most situations. With this schedule, the following occurs:
Each day, all files that have changed since the lower-level backup at the end of the previous week are saved.
For each weekday level 9 backup, the previous level 0 or level 5 backup is the closest backup at a lower level. Therefore, each weekday tape contains all the files that changed since the end of the previous week or the initial level 0 backup for the first week.
For each Friday level 5 backup, the closest lower-level backup is the level 0 backup done at the beginning of the month. Therefore, each Friday's tape contains all the files changed during the month up to that point.
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 |
The following table shows how the contents of the tapes can change across two weeks with the daily cumulative, weekly cumulative schedule. Each letter represents a different file.
Table 23–8 Contents of Tapes for Daily Cumulative/Weekly Cumulative Backup 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 |
With this schedule, you need six tapes if you want to reuse daily tapes. However, you need nine tapes if you want to use four different daily tapes:
One tape for the level 0 backup
Four tapes for Fridays
One or four daily tapes
If you need to restore a complete file system, you need the following tapes:
The level 0 tape
The most recent Friday tape
The most recent daily tape since the last Friday tape, if any