Split-Mirror Disk Backup (SAP Library - SAP Database Guide: Oracle (BC-DB-ORA-DBA))

Split-Mirror Disk Backup

Use

This section describes how you can use split-mirror disk backup with BRBACKUP to perform an online or offline backup of your Oracle database without downtime. We recommend this especially for online backup of large databases.

Caution

We provide this information on split-mirror disk backup for advice only. Consult your hardware partner for help in setting up split-mirror disk backup.

It is especially important to make sure that the data on the backup database host is consistent when you perform the backup.

Integration

Computing Center Management System (CCMS)

You cannot use CCMS to schedule split-mirror disk backups. This is because BRBACKUP runs on the backup database host.

However, you can use CCMS to monitor backups on the production database, because BRBACKUP sends status information to the production database, which CCMS can then use.

The BACKINT interface is also supported in the split-mirror configuration. This configuration is transparent to BACKINT and there are no extra considerations for BRBACKUP.

A split-mirror disk backup only includes database backups with BRBACKUP. Backups of the offline redo log files using BRARCHIVE are not included because they do not place any significant load on the production host. In a standard setup, you back up the offline redo log files on the database server to local or remote tape devices, on disk or with BACKINT.

If the backup device is connected to the backup server, you can use the remote device – using backup_dev_type = pipe|pipe_auto|pipe_box – or the BACKINT interface.

To synchronize BRBACKUP sessions with BRARCHIVE sessions, you can start a BRARCHIVE session immediately after the disks are split and not just at the end of the online BRBACKUP session. When the disks have been split, Oracle regards the backup as already finished.

Features

In the split-mirror configuration, the disks of the production database host are mirrored, that is, synchronized. BRBACKUP runs on a backup database host, where the backup is performed after the mirror disks have been split and mounted. On the production host, this saves processing power otherwise required for the backup, so that the production SAP System is unaffected by the backup.

BRBACKUP can be used to control the splitting and later synchronization of the disks. If you want to open the database on the backup host and use it as a "reporting server" you can perform the synchronization yourself later.

The actual splitting and later synchronization of disks is executed by a script or program supplied and supported not by SAP, but by the manufacturer of the operating system, disk subsystem, or backup software.

If the split disks do not have to be resynchronized immediately after the backup you can use the backup server along with the mirror disks to operate an independent SAP System on the backup server. For this you must install the entire Oracle server software on the backup server.

For more information, see the following:

To start split-mirror backup on the production database server, see SAP Note 170607.
To divide the split mirrors, see SAP Note 378818.

Activities

The following graphic shows how split-mirror backup works:

This graphic is explained in the accompanying text

As shown in the above graphic, a split-mirror backup works as follows:

	Split-Mirror Online Backup	Split-Mirror Offline Backup
1	Tablespaces set to status BACKUP	Production database shut down
2	Mirror disks (A' and B' in the graphic) split and connected to backup server using split_cmd
3	Tablespaces reset to normal status	Production database restarted
4	Mirror disks backed up on backup host
5	Primary and mirror disks resynchronized using resync_cmd

Recommendation

Consider online split-mirror disk backup if high availability is an important consideration for your system.