Frozen Image Backups

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Block Level Database Backups Using Database Editions

While database agents are very helpful in the backup process, sometimes they are just not enough. For backups of an Oracle database, VERITAS Software offers an alternative. By combining the VERITAS Database Edition for Oracle with NetBackup for Oracle Advanced BLI Agent, you can do true block-level incremental backups of your Oracle database. The VxFS Storage Checkpoint facility keeps track of data blocks modified by the database since the last backup. This is a copy-on-write snapshot facility, which we discuss in detail later in the chapter. NetBackup with BLI Backup leverages this facility to back up only changed blocks, not the entire database, for an incremental backup. A database BLI Backup is done at the filesystem block level, which means only changed blocks, not the changed files, are backed up. Because the VxFS Storage Checkpoint facility identifies changed blocks in real time, BLI Backup does not need to search the entire database for the modified blocks. BLI Backup saves time, decreases the amount of backup media required, and significantly reduces CPU and network overhead during backups. In addition, this allows more frequent backups, making backup images more up-to-date. BLI Backup supports full, as well as block-level, incremental backups of Oracle databases. When restoring Oracle database files, NetBackup restores an appropriate full backup and then applies the changed blocks from the incremental backups. This restore process is performed automatically by NetBackup and is completely transparent. In addition, BLI Backup supports both cold (offline) backup and hot (online) backup to meet database availability and performance needs.

The Advanced BLI Agent interfaces with RMAN (Recovery Manager) via the Proxy copy feature. Proxy copy requires System Backup to Tape (SBT) API 2.0, which was introduced with Oracle 8.1.5. There are two types of Storage Checkpoints: Nodata and Fulldata. The Advanced BLI Agent uses Nodata Storage Checkpoints for Proxy copy BLI backups. Nodata Storage Checkpoints will track changed VxFS filesystem blocks with a bitmap. With Nodata Storage Checkpoints, the tablespaces are kept in hot backup mode for the duration of the backup. An added benefit of using the RMAN Proxy copy feature is that backup and restore operations are managed and controlled via RMAN, thus reducing administration complexity.

If you choose not to use RMAN, the NetBackup for Oracle Advanced BLI Agent offers a script-based alternative. The script method uses both the Nodata Storage Checkpoint (described previously), as well as the Fulldata Storage Checkpoint. The Fulldata Storage Checkpoint differs from the Nodata in two ways. First, a copy of the changed filesystem block will be copied into the Storage Checkpoint before the first write change is made to the block. Second, the tablespaces are left in hot backup mode only for the amount of time it takes to create the Storage Checkpoint.

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