Testing for Availability - Expert Oracle RAC Performance Diagnostics and Tuning - page 67

Using ASM redundancy
There are three levels of redundancy supported by ASM:

1.

Normal redundancy requires three diskgroups and maintains three mirrored copies
of the OCR file.

2.

High redundancy requires five diskgroups and maintains five mirrored copies of the
OCR file.

3.

External redundancy only requires one diskgroup and relies on the storage for external
mirroring of the OCR file.

■ the diskgroup requirements for the redundancy levels when configuring oCr files during grid infrastructure
installation should not be confused with diskgroup requirements during database configuration. When configuring
diskgroups for storing data and fast recovery area (fra), normal redundancy requires two disks/logical unit numbers
(lUns) to be part of the diskgroup. high redundancy requires three disks/lUns or failure groups to be part of the
diskgroup. external redundancy requires one disk/lUn to be part of the diskgroup.

Note

Multiplexing
By configuring individual diskgroups and adding OCR files manually using the ocrconfig command, redundant
copies of the OCR file can be maintained. With this file, two physical OCR files are maintained in parallel across two
different diskgroups.

[root@prddb1 ~]# $GRID_HOME/bin/ocrcheck
Status of Oracle Cluster Registry is as follows :
Version : 3
Total space (kbytes) : 262120
Used space (kbytes) : 2964
Available space (kbytes) : 259156
ID : 1549014030
Device/File Name : +PRDDB_GRID1
Device/File integrity check succeeded
Device/File Name : +PRDDB_GRID2
Device/File integrity check succeeded
Device/File not configured
Device/File not configured
Device/File not configured
Cluster registry integrity check succeeded

Media Failure
Media failures comprise the failure of the various components of the database, such as data files, tablespaces, and the
entire database itself. They occur when the Oracle file storage media is damaged and prevents Oracle from reading
or writing data, resulting in the loss of one or more database files. These failures could affect one or all types of files
necessary for the operation of an Oracle database, including online redo log files, archived redo log files, and control files.