This section describes the lifecycle of a backup as it flows through the Recovery Appliance environment depicted in Figure 2-1. In this sample scenario, each protected database has already seeded Recovery Appliance with the required initial level 0 incremental backup. The basic data flow is as follows:

1. A protected database, or a standby database protecting this database, sends a level 1 incremental backup to the Recovery Appliance.

   Recovery Appliance distinguishes itself from other backup solutions because only one level 0 backup is ever required for each data file. Level 1 incremental backups are most efficient because data blocks are only backed up when they change.

   Oracle recommends making cumulative level 1 incremental backups (see Oracle Database Backup and Recovery Reference). Each cumulative level 1 backup uses the most recent virtual level 0 backup as its baseline. Typically, this virtual level 0 backup corresponds to the most recent level 1 backup.

   Note:

   If a level 1 cumulative backup cannot be incorporated into the Recovery Appliance (for example, because of a storage corruption), then the next level 1 backup has the same virtual level 0 backup baseline, enabling the Recovery Appliance to seamlessly incorporate the new level 1 incremental backup. Thus, cumulative backups almost never have greater overhead than differential backups.

2. The Recovery Appliance receives the incremental backup.

   The received backup is available for immediate retrieval, but the Recovery Appliance has not yet indexed it, so the corresponding virtual full backups are not available. If a protected database requires this backup for recovery before the Recovery Appliance can index it, then RMAN automatically restores the previous virtual full backup and applies this incremental backup to it.

3. The Recovery Appliance processes the incremental backup.

   The following operations occur asynchronously:

   • The Recovery Appliance performs backup ingest. The Recovery Appliance processes the backup as follows:

     • Scans the backup that was sent by a protected database

     • Breaks it into smaller groups of blocks, assigning the blocks from each data file to a separate delta pool

     • Writes the groups into the appropriate storage location according to the protection policy for the database

     • Deletes the original backup set after the virtual backup set has been created

       Note:

       The Recovery Appliance may not delete the original backup at precisely the same time that the virtual backup is created. Thus, it is possible for both the original and virtual backups to coexist briefly in the recovery catalog as two separate copies.

     During backup ingest, the Recovery Appliance also indexes the backup, which involves storing information about the contents and physical location of each data block in the metadata database. Because the Recovery Appliance contains the recovery catalog for the protected database, the newly indexed virtual full backups are now available for use by RMAN, if needed for recovery.

   • If Recovery Appliance replication is configured, then the Recovery Appliance forwards the backup to a downstream Recovery Appliance.

     Many different replication configurations are possible. Figure 2-1 shows a one-to-one configuration in which the central Recovery Appliance, acting as the upstream Recovery Appliance (backup sender), forwards its backups to a separate Recovery Appliance, acting as the downstream Recovery Appliance (backup receiver). Figure 2-1 shows cascaded replication, in which the downstream Recovery Appliance forwards its backups to a third Recovery Appliance.

   • If automated copy-to-tape policies are enabled, then the Recovery Appliance archives the backup to tape.

     In Figure 2-1, the central Recovery Appliance uses Oracle Secure Backup software to communicate with a tape device. Also, the Recovery Appliance furthest downstream in the replication scheme archives its backups to tape. This technique has the following benefits:

     • To create redundancy, identical backups reside on two separate tape devices. In Figure 2-1, the primary Recovery Appliance archives to tape, as does the Recovery Appliance that is furthest downstream.

     • A downstream Recovery Appliance can back up to tape, thus offloading tape archival processing from the upstream Recovery Appliance.

   • The Recovery Appliance periodically verifies that backups and redo are valid.

     The Recovery Appliance automatically validates backups on disk, and during inbound and outbound replication. The Recovery Appliance automatically performs crosschecks of tape backups. Just as with data file backups, the Recovery Appliance validates the integrity of redo log blocks during every operation, including receiving redo from protected databases and storing it in compressed archived log backup sets. No manually run RMAN VALIDATE commands are required.

   • The Recovery Appliance performs automated delta pool space management.

     This phase involves deleting obsolete and expired backups, both on disk and tape, and optimizing the delta pools.