In 11gR2 ASM diskgroups are used 1) by Grid infrastructure for the OCR, Voting disk and the ASMspfile. 2) by the database for DATA and FRA.
ASM redundancy levels, can be a bit misleading in Oracle 11gR2 compared to 10gR2. They are called the same, Normal redundancy, High Redundancy and External Redundancy. However, depending on what area of the 11gR2 configuration this will be used, the number of disks required to configure are not the same. DBA’s seldom are able to take the difference into consideration when requesting disks /LUN’s from the storage administrators and are taken by surprise during installation.
Grid Infrastructure: When configuring diskgroups for the OCR file, voting disk and ASMspfile, Normal redundancy requires 3 disks/LUNS to be part of the diskgroup. High redundancy requires 5 disks/LUNS to be part of the diskgroup. External redundancy requires just one disk/LUN to be part of the diskgroup. The below screen output shows the error message when only one disk/LUN is selected for the GRID diskgroup.
Database: When configuring diskgroups for DATA and FRA, normal redundancy requires 2 disks/LUNS to be part of the diskgroup. High redundancy requires 3 disks/LUNs or failure groups to be part of the diskgroup. External redundancy requires just one disk/LUNs or failure groups to be part of the diskgroup
More about configuring OCR and voting disks in the next post.