Backup Levels

Because it may not be practical or efficient for you to run a full level backup every day, Backup enables you to specify the level of the backup operation performed during its automatic, scheduled group backups. Limiting how often you perform a full backup can help maintain server efficiency, while still ensuring that your data is protected. Different backup levels enable you to trade off the number of volumes and amount of time required to complete a backup with the number of volumes and amount of time required to recover from a disk crash.

Backup supports four kinds of backup levels for filesystem data:

• Full - backs up all files, regardless of whether they have changed.

• Level 1-9 - backs up files that have changed since the last lower numbered backup level, the last full backup being considered a level zero. For example, a level 1 backs up all the files that have changed since the last full backup (considered a level zero). A level 3 backs up all the files that have changed since the last level 2, level 1, or full backup. A level 9 backs up all the files that have changed since the last level 8, 7, 6, 5, 4, 3, 2, 1, or full backup.

• Incremental - backs up files that have changed since the last backup, regardless of the level.

• Skip - skips the scheduled backup. For example, you may want to skip a backup on a holiday if you know that no one is available to change or add more volumes.

How Backup Uses Backup Levels

A backup schedule defines what level backup should be done on a given day during a backup cycle. You can apply one or more of these backup levels to customize a backup schedule. If you are considering using backup levels in a customized schedule, consider the following issues to help you make decisions that best suit your environment:

• Full backups take more time to complete than incremental backups.

• If you have only one storage device and the full backup does not fit on a single piece of media, an operator must be available to monitor the backup and change the media.

• Full backups cause the online indexes to grow more rapidly than incremental or level backups.

• Level backups serve as checkpoints in your schedules because they collect all the files that have changed over several days, or even weeks, into a single backup session. Using level backups can simplify and speed file recovery.

The online client file indexes, server index, and media database are backed up whenever the Backup server is backed up. In general, they take on the backup level of the server. For example, if the Backup server's backup is a full level, the backup of the online client file indexes, server index, and media database is also a full level; if the Backup server's backup is a level 5, the backup of the online client file indexes, server index, and media database is also a level 5. However, when the server's backup level is incremental, the backup of the online client file indexes, server index, and media database is level 9.

How Backup Levels Work

Backup levels work in conjunction with a client's backup schedule. The way you define the backup levels directly affects how long the recovery from a disk crash takes and how many backup volumes you need.

The following paragraphs, accompanied by graphics, illustrate the concept of how Backup backup levels work and the data requirements for recovery in the event of data loss.

On October 2, a full backup runs. On October 3, the incremental backup saves everything that changed since the full backup. On October 4, the incremental backup backs up everything that changed since the 3rd. On October 5, the level 7 backup backs up everything that changed since the full backup. To fully recover from a disk crash on October 5, you need only two volumes: the full volume and the level 7 volume. You no longer need the data on the volumes from October 3 and 4, because the level 7 volume includes that information. (See Figure 3-5.)

Figure 3-5 Example: Backups for October 2 through October 8

On October 6, 7, and 8, the incremental backup backs up everything that has changed since the level 7 backup. On October 9, as shown in Figure 3-6, the level 5 backup backs up everything that changed since the full backup. To fully recover from a disk crash on October 9, you need only two volumes: the full volume and the level 5 volume. You no longer need the data on the volume from the level 7 backup or the subsequent incremental backups because the level 5 volume includes that information.

Figure 3-6 Example: Backups for October 2 through October 15

On October 12, the level 7 backup backs up all the data that changed since the last lower numbered backup, in this case the level 5 backup from October 9. To recover from a disk crash on October 12, you need three volumes: the full volume, the level 5 volume, and the new level 7 volume. (See Figure 3-6.)

On October 16, the level 5 backup backs up all the data that changed since the last lower numbered backup. Because no lower numbered level backup has been performed (for example, levels 1 - 4), the level 5 backup backs up all the data that changed since the full backup. To recover from a disk crash on October 16, you need two volumes: the full volume and the new level 5 volume. (See Figure 3-7.)

Figure 3-7 Example: Backups for October 2 through October 16

Level 1-9 backups help you maintain control over the number of volumes you use. A carefully thought-out backup strategy enables you to recover everything to disk with a minimum number of volumes. The fewer volumes you need to recover from a disk crash, the less time you must spend restoring the disk.

You can also control the size and time it takes to back up your data by using directives, which compress and eliminate unnecessary data from your backups. For example, you can use a directive that tells Backup to skip certain files or filesystems when performing a backup. For more information on directives, see "What Are Directives? ".