7 Managing Backup and Recovery

Restoring Backups from a Cluster File System

The scheme that this section describes assumes that you are using the "Oracle Automatic Storage Management and Cluster File System Archiving Scheme". In this scheme, assume that node3 performed the backups to a cluster file system. If node3 is available for the restore and recovery operation, and if all of the archived logs have been backed up or are on disk, then run the following commands to perform complete recovery:

RESTORE DATABASE;
RECOVER DATABASE;

If node3 performed the backups but is unavailable, then configure a media management device for one of the remaining nodes and make the backup media from node3 available to this node.

run {
ALLOCATE CHANNEL DEVICE TYPE sbt C1 CONNECT '@racinst_1'
ALLOCATE CHANNEL DEVICE TYPE sbt C2 CONNECT '@racinst_2'
...
}

Restoring Backups from a Noncluster File System

The scheme that this section describes assumes that you are using the "Noncluster File System Local Archiving Scheme". In this scheme, each node archives locally to a different directory. For example, node1 archives to /arc_dest_1, node2 archives to /arc_dest_2, and node3 archives to /arc_dest_3. You must configure a network file system file so that the recovery node can read the archiving directories on the remaining nodes.

If all nodes are available and if all archived redo logs have been backed up, then you can perform a complete restore and recovery by mounting the database and running the following commands from any node:

RESTORE DATABASE;
RECOVER DATABASE;

Because the network file system configuration enables each node read access to the redo log files on other nodes, then the recovery node can read and apply the archived redo logs located on the local and remote disks. No manual transfer of archived redo logs is required.

Using RMAN or Oracle Enterprise Manager to Restore the Server Parameter File (SPFILE)

RMAN can restore the server parameter file either to the default location or to a location that you specify.

You can also use Oracle Enterprise Manager to restore the SPFILE. From the Backup/Recovery section of the Maintenance tab, click Perform Recovery. The Perform Recovery link is context-sensitive and navigates you to the SPFILE restore only when the database is closed.

Single Node Failure in Oracle RAC

Instance recovery in Oracle RAC does not include the recovery of applications that were running on the failed instance. Oracle Clusterware restarts the instance automatically.

Applications that were running on a node before it failed continue running by using failure recognition and recovery. This provides consistent and uninterrupted service if hardware or software fails. When one instance performs recovery for another instance, the surviving instance reads online redo logs generated by the failed instance and uses that information to ensure that committed transactions are recorded in the database. Thus, data from committed transactions is not lost. The instance performing recovery rolls back transactions that were active at the time of the failure and releases resources used by those transactions.

Multiple-Node Failures in Oracle RAC

When multiple node failures occur, if one instance survives, then Oracle RAC performs instance recovery for any other instances that fail. If all instances of an Oracle RAC database fail, then Oracle Database automatically recovers the instances the next time one instance opens the database. The instance performing recovery can mount the database in either cluster database or exclusive mode from any node of an Oracle RAC database. This recovery procedure is the same for Oracle Database running in shared mode as it is for Oracle Database running in exclusive mode, except that one instance performs instance recovery for all of the failed instances.

Using RMAN to Create Backups in Oracle RAC

Oracle Database provides RMAN for backing up and restoring the database. RMAN enables you to back up, restore, and recover data files, control files, SPFILEs, and archived redo logs. RMAN is included with the Oracle Database server and it is installed by default. You can run RMAN from the command line or you can use it from the Backup Manager in Oracle Enterprise Manager. In addition, RMAN is the recommended backup and recovery tool if you are using Oracle Automatic Storage Management (Oracle ASM). The procedures for using RMAN in Oracle RAC environments do not differ substantially from those for Oracle noncluster environments.

CONFIGURE DEVICE TYPE sbt PARALLELISM 3;
CONFIGURE DEFAULT DEVICE TYPE TO sbt;
CONFIGURE CHANNEL DEVICE TYPE SBT CONNECT 'dbauser/pwd@service_name'

CONFIGURE DEVICE TYPE sbt PARALLELISM 3;
CONFIGURE CHANNEL 1.. CONNECT 'dbauser/pwd@mydb_1';
CONFIGURE CHANNEL 2.. CONNECT 'dbauser/pwd@mydb_2';
CONFIGURE CHANNEL 3.. CONNECT 'dbauser/pwd@mydb_3';

RUN
{
    ALLOCATE CHANNEL CH1 CONNECT 'dbauser/pwd@mydb_1';
    ALLOCATE CHANNEL CH2 CONNECT 'dbauser/pwd@mydb_2';
    ALLOCATE CHANNEL CH3 CONNECT 'dbauser/pwd@mydb_3';
    BACKUP DATABASE PLUS ARCHIVED LOG;
}

Node Affinity Awareness of Fast Connections

In some cluster database configurations, some nodes of the cluster have faster access to certain data files than to other data files. RMAN automatically detects this situation, which is known as node affinity awareness. When deciding which channel to use to back up a particular data file, RMAN gives preference to the nodes with faster access to the data files that you want to back up. For example, if you have a three-node cluster, and if node1 has faster read/write access to data files 7, 8, and 9 than the other nodes, then node1 has greater node affinity to those files than node2 and node3.

Deleting Archived Redo Logs after a Successful Backup

If you have configured the automatic channels as defined in section "Channel Connections to Cluster Instances with RMAN", then you can use the following example to delete the archived logs that you backed up n times. The device type can be DISK or SBT:

DELETE ARCHIVELOG ALL BACKED UP n TIMES TO DEVICE TYPE device_type;

During a delete operation, if at least one channel allocated has access to the archived log, then RMAN automatically schedules the deletion of the specific log on that channel. For a local archiving scheme, there must be at least one channel allocated that can delete an archived log. For a cluster file system archiving scheme, assuming that every node writes to the archived logs on the same cluster file system, the archived log can be deleted by any allocated channel.

If you have not configured automatic channels, then you can manually allocate the maintenance channels as follows and delete the archived logs.

ALLOCATE CHANNEL FOR MAINTENANCE DEVICE TYPE DISK CONNECT 'SYS/oracle@node1';
ALLOCATE CHANNEL FOR MAINTENANCE DEVICE TYPE DISK CONNECT 'SYS/oracle@node2';
ALLOCATE CHANNEL FOR MAINTENANCE DEVICE TYPE DISK CONNECT 'SYS/oracle@node3';
DELETE ARCHIVELOG ALL BACKED UP n TIMES TO DEVICE TYPE device_type;

Autolocation for Backup and Restore Commands

RMAN automatically performs autolocation of all files that it must back up or restore. If you use the noncluster file system local archiving scheme, then a node can only read the archived redo logs that were generated by an instance on that node. RMAN never attempts to back up archived redo logs on a channel it cannot read.

During a restore operation, RMAN automatically performs the autolocation of backups. A channel connected to a specific node only attempts to restore files that were backed up to the node. For example, assume that log sequence 1001 is backed up to the drive attached to node1, while log 1002 is backed up to the drive attached to node2. If you then allocate channels that connect to each node, then the channel connected to node1 can restore log 1001 (but not 1002), and the channel connected to node2 can restore log 1002 (but not 1001).

Parallel Recovery with RMAN

With RMAN's RESTORE and RECOVER commands, Oracle Database automatically makes parallel the following three stages of recovery:

Restoring Data Files When restoring data files, the number of channels you allocate in the RMAN recover script effectively sets the parallelism that RMAN uses. For example, if you allocate five channels, you can have up to five parallel streams restoring data files.

Applying Incremental Backups Similarly, when you are applying incremental backups, the number of channels you allocate determines the potential parallelism.

Applying Archived Redo Logs With RMAN, the application of archived redo logs is performed in parallel. Oracle Database automatically selects the optimum degree of parallelism based on available CPU resources.

Disabling Parallel Recovery

You can override parallel recovery using the procedures under the following topics:

• Disabling Instance and Crash Recovery Parallelism

• Disabling Media Recovery Parallelism