Developers Guide

Components of ASM
12 Dell EMC SC Series Storage with Oracle ASM | CML1111
groups with different redundancy settings and fail-groups if necessary. It is recommended to have at least the
following disk groups:
• Database data (DATA): Where active database files such as data files, control files, online redo logs,
archive redo logs, and change-tracking files used in incremental backups are stored.
• Flash Recovery Area (FRA): Where recovery-related files are created, such as multiplexed copies of
the current control file and online redo logs, backup sets, and flashback log files.
3.3.1 ASM disk group redundancy
There are three types of redundancy for ASM disk groups:
• Normal Redundancy: Provides 2-way mirrored redundancy which requires two ASM failure groups.
This is the default.
• High Redundancy: Provides 3-way mirrored redundancy which requires three ASM failure groups.
• External Redundancy: Provides no protection within ASM. Since ASM does not provide redundancy
when external redundancy is used, the server CPU and other resources are less consumed, which
means there is an increase of available CPU cycles for database operations. This level of redundancy
requires RAID protection on the storage arrays. This is generally the recommended redundancy level
when using SC Series storage. There are use cases in Oracle ASM that might require either normal
or high redundancy even if SC Series storage is used. SC Series storage provides redundancy at the
storage (disks) level. If a database server cannot access the ASM LUN at the operating-system level
due to operating-system errors, the ASM instance will fail. If this is a primary concern, configure the
ASM disk group with normal redundancy (with two failure groups), or high redundancy. If extended
distance clusters are a primary objective, either normal or high redundancy levels must be chosen.