||Oracle Tips by Burleson
10g Grid Computing
Preparing Shared Storage
Overview of the Files and Directories Required
Bottom line is that all the participating
instances of an Oracle RAC database must have access to the shared
data files, redo log files and control files. At the same time, the
physical host level cluster consisting of physical nodes needs to
have shared access to the quorum disk, voting disk and OCR file. If
you are using the vendor provided cluster manager, you may still
need the appropriate quorum disk as prescribed in the cluster
manager software. The Oracle provided Cluster Ready Services (CRS)
need voting disks and OCR files. There are other files, which may
need to be shared. They include the files supporting the external
tables. It is also recommended to have the archive log files
destination on a shared file system.
The Following Diagram (Fig. 5.2) shows a
collection of all the components that make up the RAC File
structures. This diagram will provide us a road map for discussion
as to how we can prepare these structures before we embark on
creating the database and launch the database instances.
Figure 5.2 All the Physical File Structures of the RAC Database
Of the files that we have shown above, most of
them need to be on shared storage. There are some files that can be
on a local file system, but it is recommended that they are placed
on a shared file system. There are some file structures, which can
very well reside on a local file system.
Let’s look at these three combinations:
1. The following files reside on Shared
Storage and are accessible by all the RAC instances at the same
Data Files, which make up the main data
storage file structures
Parameter File (SPFILE) - Maintains a
common spfile located on shared file system that is accessible
to all the instances of the RAC database.
Password File that maintains the
Voting Disk File and OCR files that are
used by the cluster ready services.
2. The following files reside on Shared
Storage and are accessible by a specific instance. However, under
certain conditions like recovery etc., the files need to be
available for other instances also.
Redo Log Files that record the instance
specific transaction changes.
Files supporting the Undo Tablespace, used
by a specific instance to maintain the read consistency
Archive Log Files that are the saved redo
Files supporting the External Tables –
External Tables are logical database objects that are accessible
to all the instances.
3. The following are file structures, which
are created, accessed and managed by a specific instance.
Alert Log File - keeps a running log of
database changes and events.
Trace Files that provide detailed
information about the database events.
Oracle Executables (Oracle Home Files).
Oracle Cluster Ready Services (CRS) Home,
which has all the binaries supporting the CRS.
However, note that with the use of the cluster
file system it is possible to use a Shared Oracle Home and shared
CRS Home. When using the cluster file system such as HP’s Tru64 CFS,
Veritas CFS, Polyserve Matrix Server, you can maintain a single
Oracle Home and share it among all the nodes of the cluster.
While talking about the shared file structures,
there are four combinations as shown in the Fig. 5.3.
Figure 5.3 Shared Storage Inputs
They can be on raw devices.
They can be on a Cluster File System
(CFS). CFSs concurrently mounted on all the participating nodes of
They can be accessed via the
Automatic Storage Management (ASM) instance.
They can be located on Network File
Even though we have listed three types of
shared storage structures, it is also possible to mix them so that
some shared files can be on raw devices, some can locate on CFS and
some can come out of ASM.
The above text is
an excerpt from:
Oracle 10g Grid & Real Application
Computing with RAC
by Mike Ault, Madhu Tumma
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