Guidelines for Scheduling Backups

A backup schedule is the schedule you establish to run the ufsdump command. This section provides guidelines on the factors to weigh when creating a backup schedule, guidelines on how often to back up file systems, and sample backup schedules.

What Drives a Backup Schedule

The schedule you create depends on:

• Your need to minimize the number of tapes

• Time available for doing backups

• Time available to do a full restore of a damaged file system

• 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 media spent on backups, you can do full backups every day. However, this is not realistic for most sites, so incremental backups are used most often. In this case, you should back up your site enough to restore files from the last four weeks. This requires at least four sets of tapes--one for each week, which you would reuse each month. In addition, you should archive the monthly backups for at least a year, and then keep yearly backups for a number of years.

Using Dump Levels to Create Incremental Backups

The dump level you specify in the ufsdump command (0-9) determines which files are backed up. Specifying dump level 0 creates a full backup. Numbers 1-9 are used to schedule incremental backups, but have no defined meanings. Numbers 1-9 are just a range of numbers 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.

The following examples show the flexibility of the incremental dump procedure using levels 1-9.

Dump Levels for Daily, Cumulative Backups

Doing daily, cumulative incremental backups is the most commonly used backup scheme and is recommended for most situations. The following example shows a schedule using a level 9 dump each day, and a level 5 dump on Friday to restart the process.

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

Figure 42-1 Incremental Backup: Daily Cumulative

Dump Levels for Daily, Discrete Backups

The following example shows a schedule where you capture only a day's work on different tapes. In this case, sequential dump level numbers are used during the week (3,4,5,6) with a lower number (2) on Friday.

In the following 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 high/low sequence.

Figure 42-2 Incremental Backup: Daily Discrete