Database Reference
In-Depth Information
Flex ASM Architecture
Oracle Flex ASM Architecture
In 11gR2 or earlier ASM architecture or the standard 12c ASM, the ASM instance runs on every RAC node and the
RAC databases have to rely on the ASM instance on the local node to do the storage I/O. This requirement has several
limitations:
Requiring ASM instance running on every RAC instance consumes CPU and memory resources on each RAC
node.
All Database instances on each node depend on the local ASM instance. The ASM instance failure will cause all
local database instances to fail.
Oracle Flex ASM introduced in Oracle 12cR1 removes these two limitations. In Oracle Flex ASM architecture, only
a small number of cluster nodes run Oracle ASM instances. These ASM instances are connected by all the database
instances on the cluster to provide storage access to these database instances. When an ASM instance fails, the
database instances that connected to the failed ASM instance reconnect to other ASM instances.
Oracle Flex ASM is an option in Oracle 12c ASM which you can enable or disable. If you choose to disable the Flex
ASM feature, your cluster is a standard ASM cluster which is same as the ASM in 11gR2 or before, in which there is an
ASM instance running on each RAC node and all the database instances have to access a local Oracle ASM instance.
If you choose to enable the Flex ASM feature in your cluster, the ASM configuration on your cluster becomes a
Flex ASM. In this case, your cluster will have two kinds of nodes: those that have an ASM instance and those that don't
have an ASM instance. Figure 4-5 shows a four-node Flex ASM configuration where three RAC nodes run Oracle ASM
instances, which is set by default and can be reset with a cardinality setting. Node 4 doesn't have an ASM instance,
and the database instance on node 4 connects to the ASM instance on node 1 for ASM service.
Node1
Node2
Node3
Database
Instance 2
Grid Infrasturecture
Database
Instance 1
Grid Infrasturecture
Database
Instance 3
Grid Infrasturecture
ASM
Instance
ASM
Instance
ASM
Instance
Clusterware
Clusterware
Clusterware
Node4
Database
Instance 4
Grid Infrasturecture
ASM Disk
Groups
Clusterware
Shared Storage
Figure 4-5. An Oracle Flex ASM configuration example
 
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