Choosing a Tape Device

The following table shows typical tape devices that are used for storing file systems during the backup process. The storage capacity depends on the type of drive and the data being written to the tape. For more information on tape devices, see Chapter 52, Managing Tape Drives (Tasks).

Table 46-5 Typical Media for Backing Up File Systems

High-Level View of Backing Up and Restoring File Systems (Task Map)

Use this task map to identify all the tasks for backing up and restoring file systems. Each task points to a series of additional tasks, such as determining the type of backup to perform.

Guidelines for Scheduling Backups

A backup schedule is the schedule that you establish to run the ufsdump command. This section discusses guidelines on the factors to weigh when you create a backup schedule. This section also includes sample backup schedules.

The backup schedule that you create depends on the following:

• Your need to minimize the number of tapes that are used for backups

• The time available for doing backups

• The time available for doing a full restore of a damaged file system

• The time available for retrieving individual files that are accidentally deleted

How Often Should You Do Backups?

If you do not need to minimize time and the number of media that is used for backups, you can do full backups every day. However, this backup method is not realistic for most sites, so incremental backups are used most often. In this case, you should back up your site enough to so that you can restore files from the last four weeks. This schedule requires at least four sets of tapes, one set for each week. You would then reuse the tapes each month. In addition, you should archive the monthly backups for at least a year. Then, keep yearly backups for a number of years.

Backup Terms and Definitions

The following table describes backup terms and definitions.

Suggestions for Scheduling Backups

The following table provides other suggestions for scheduling backups.

Table 46-6 Suggestions for Backup Schedules

Using Dump Levels to Create Incremental Backups

The dump level you specify in the ufsdump command (0-9) determines which files are backed up. Dump level 0 creates a full backup. Levels 1-9 are used to schedule incremental backups, but have no defined meanings. Levels 1-9 are just a range of numbers that are used to schedule cumulative or discrete backups. The only meaning levels 1-9 have is in relationship to each other, as a higher or lower number. A lower dump number always restarts a full or a cumulative backup. The following examples show the flexibility of the incremental dump procedure using levels 1-9.

Example--Dump Levels for Daily, Cumulative Backups

Doing daily, cumulative incremental backups is the most commonly used backup schedule and is recommended for most situations. The following example shows a schedule that uses a level 9 dump Monday through Thursday, and a level 5 dump on Friday to restart the process.

Figure 46-1 Incremental Backup: Daily Cumulative

In the preceding example, you could have used other numbers in the 1-9 range to produce the same results. The key is using the same number Monday through Thursday, with any lower number on Friday. For example, you could have specified levels 4, 4, 4, 4, 2 or 7, 7, 7, 7, 5.

Example--Dump Levels for Daily, Incremental Backups

The following example shows a schedule where you capture only a day's work on different tapes. This type of backup is referred to as a daily, incremental backup. In this case, sequential dump level numbers are used during the week (3, 4, 5, 6) with a lower number (2) on Friday. The lower number on Friday restarts the processing.

Figure 46-2 Incremental Backup: Daily Incremental

In the preceding example, you could have used the sequence 6, 7, 8, 9 followed by 2, or 5, 6, 7, 8 followed by 3. Remember, the numbers themselves have no defined meaning. You attribute meaning by ordering them in a specified sequence, as described in the examples.

Sample Backup Schedules

This section provides sample backup schedules. All schedules assume that you begin with a full backup (dump level 0), and that you use the -u option to record each backup in the /etc/dumpdates file.

Example--Daily Cumulative, Weekly Cumulative Backups

Table 46-7 shows the most commonly used incremental backup schedule. This schedule is recommended for most situations. With this schedule, the following occurs:

• 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 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.

Table 46-7 Daily Cumulative or Weekly Cumulative Backup Schedule

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 46-8 Contents of Tapes for Daily Cumulative/Weekly Cumulative Backup Schedule