Oracle Clusterware is required
As stated by Oracle’s documentation, “Oracle
Clusterware is a requirement for using Oracle
11g RAC, and it is the only clusterware that you
need for most platforms.
Although Oracle 11g RAC continues to
support select third-party clusterware products
on specific platforms, you MUST also install and
use Oracle Clusterware.”
The Oracle Universal Installer
(OUI) installs clusterware on each node.
The clusterware home is called CRS home.
The CRS home is distinct from the RAC-enabled
Oracle home. The CRS home can be shared by one
or more nodes, or be private to each node.
Vendor clusterware may be installed with Oracle
Clusterware for all UNIX-based operating systems
The Oracle Cluster Registry
(OCR) contains cluster and database
configuration information for RAC Cluster Ready
(CRS), including the list of nodes in the
cluster database, the CRS application, resource
profiles, and the authorizations for the Event
The OCR can reside in a file on a cluster file
system or on a shared raw device.
Raw devices will not be supported in
future versions of Oracle (Metalink 578455.1).
The clusterware software is installed in the
cluster with its own set of binaries. The CRS
Home and Oracle Home are in different locations.
The clusterware software installs both the
Voting Disk file and the OCR file. Installation
of clusterware configures the Virtual IP
interface. CRS resources can also be managed by
Clusterware has many daemon processes. They are
– The CRS Daemon is the main background
process for managing the HA operation of the
service. It manages the application
resources defined within the cluster. It
also maintains the configuration profiles
stored in the Oracle Configuration
Process will restart upon failure.
– Process that manages the Cluster
Synchronization Services (CSS) daemon.
Manages cluster node membership and runs as
oracle user. Failure of this
process results in cluster restart.
Failure of OCSSD causes a node
– This is event management logger. It
monitors the message flow between the nodes
and logs the relevant event information to
the log files.
– Cluster process monitor.
This process only runs on platforms
that do not use added third-party vendor
Cluster Private Interconnect
The cluster private interconnect is a high
bandwidth, low latency communication facility
that connects each node to other nodes in the
cluster and routes messages among the nodes. It
is a key component in building the RAC system.
The Oracle RAC cluster interconnect is used for
the following high-level functions:
Monitoring Health, Status, and Synchronize
Transporting lock management or resource
Moving the cache buffers (data blocks) from
node to node
High performance database computing involves
distributing the processing across an array of
cluster nodes. It requires that the cluster
interconnect provide high-data rates and
low-latency communication between node
The interconnect technology that is employed
while connecting RAC Nodes should be scalable to
handle the amount of traffic generated by the
cache synchronization mechanism. This is
directly related to the amount of contention
created by the application. The more
inter-instance updates and inter-instance
transfers there are, the more message traffic
generated. It is advisable to implement the
highest bandwidth/lowest latency interconnect
that is available for a given platform.
If the server vendor and budget supports
it, consider InfiniBand
or 10 Gigabit Ethernet.
The volume of synchronization traffic directly
impacts the bandwidth requirement. The
interconnect is not something that should be
The next section will help define the difference
between a database and database instance.
Understanding the difference is important in
order to appreciate Oracle RAC.