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Oracle10g Grid Computing with RAC
Chapter 13 - Oracle RAC Backup and Recovery

Recovery in a Raw File System Environment

The use of a clustered file system is highly recommended because it is easier to manage, backup, and restore. In a RAW file system, the archive logs from each of the nodes are not available to any of the other nodes for recovery, unless some form of log copy procedure (scripted and run through a system-scheduling program) is employed, or all of the other node’s archive log locations are NFS-mounted to the node performing the recovery operation.

If the NFS mounting scheme is used and one or more nodes are not available, then only an incomplete recovery can be performed, up to the first unavailable archive log. Even in a NFS scheme, it is suggested that some form of log copy script be used to allow the unavailable node’s logs to be available for recovery. The frequency of log copying should be based on the required concurrency of your database. If you can only afford to lose 15 minutes worth of data, then you better have all archive logs available up to the last fifteen-minute interval before the media failure.

Using RMAN, a recovery using a single tape looks identical to a single-tape recovery in the OCFS environment: 

CONFIGURE DEVICE TYPE sbt PARALLELISM 1;
CONFIGURE DEFAULT DEVICE TYPE TO sbt;
RESTORE DATABASE;
RECOVER DATABASE;

However, this assumes all of the archived redo logs are available. If all of the logs are not available, then an RMAN script similar to the following would be used to recover until the first unavailable log (in the example log sequence 2245 in thread 2 is the first unavailable log) is encountered.

RUN
{
      SET UNTIL LOG SEQUENCE 2245 THREAD 2'
      RESTORE DATABASE;
      RECOVER DATABASE;
}
ALTER DATABASE OPEN RESETLOGS;

Notice the use of the alter command to open the database. The resetlogs option resets the archive log sequences and renders previous archive logs unusable for most recovery scenarios.

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