Database Reference
In-Depth Information
Clusterware 12cR1 and Its Components
Before Oracle 11gR2, Oracle Clusterware was a distinct product installed in a home directory separate from Oracle
ASM and Oracle RAC database. Like Oracle 11gR2, in a standard 12cR1 cluster, Oracle Clusterware and Oracle ASM
are combined into a product called Grid Infrastructure and installed together as parts of the Grid Infrastructure to a
single home directory. In Unix or Linux environments, some part of the Grid Infrastructure installation is owned by
the root user and the rest is owned by special user grid other than the owner of the Oracle database software oracle.
The grid user also owns the Oracle ASM instance.
Only one version of Oracle Clusterware can be active at a time in the cluster, no matter how many different
versions of Oracle Clusterware are installed on the cluster. The clusterware version has to be the same as the Oracle
Database version or higher. Oracle 12cR1 Clusterware supports all the RAC Database versions ranging from 10gR1 to
12cR1. ASM is always the same version as Oracle Clusterware and can support Oracle Database versions ranging from
10gR1 to 12cR1.
Oracle 12cR1 introduced Oracle Flex Cluster and Flex ASM. The architecture of Oracle Clusterware and Oracle
ASM is different from the standard 12cR1 cluster. We will discuss Oracle Flex Cluster and Flex ASM in Chapter 5. This
chapter will focus on the standard 12cR1 cluster.
Storage Components of Oracle Clusterware
Oracle Clusterware consists of a storage structure and a set of processes running on each cluster node. The storage
structure consists of two pieces of shared storage: the Oracle Cluster Registry (
OCR
) and voting disk (VD) plus two local
files, the Oracle Local Registry (
OLR
) and the Grid Plug and Play (
GPnP
) profile.
OCR
is used to store the cluster configuration details. It stores the information about the resources that Oracle
Clusterware controls. The resources include the Oracle RAC database and instances, listeners, and virtual IPs (
VIPs
)
such as SCAN VIPs and local VIPs.
The voting disk (VD) stores the cluster membership information. Oracle Clusterware uses the VD to determine
which nodes are members of a cluster. Oracle Cluster Synchronization Service daemon (
OCSSD)
on each cluster node
updates the VD with the current status of the node every second. The VD is used to determine which RAC nodes are
still in the cluster should the interconnect heartbeat between the RAC nodes fail.
Both OCR and VD have to be stored in a shared storage that is accessible to all the servers in the cluster. They can
be stored in raw devices for 10g Clusterware or in block devices in 11gR1 Clusterware. With 11g R2 and 12cR1 they
should be stored in an ASM disk group or a cluster file system for a freshly installed configuration. They are allowed
to be kept in raw devices and block devices if the Clusterware was just being upgraded from 10g or 11gR1 to 11gR2;
however, it is recommended that they should be migrated to an ASM disk group or a cluster file system soon after
the upgrade. If you want to upgrade your Clusterware and Database stored in raw devices or block devices to Oracle
Clusterware 12c and Oracle Database 12c, you must move the database and OCR/VDs to ASM first before you do the
upgrade, as Oracle 12c no longer supports the use of raw device or block storage. To avoid single-point-of failure, Oracle
recommends that you should have multiple OCRs, and you can have up to five OCRs. Also, you should have at least three
VDs, always keeping an odd number of the VDs. On Linux, the
/etc/oracle/ocr.loc
file records the OCR location:
$ cat /etc/oracle/ocr.loc
ocrconfig_loc=+VOCR
local_only=FALSE
In addition, you can use the following command to find the VD location:
$ ./crsctl query css votedisk
The Oracle ASM disk group is the recommended primary storage option for OCR and VD. Chapter 5 includes a
detailed discussion of storing OCR and VDs in an ASM disk group.
