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Cluster File System (CFS) offers
a very good shared storage facility for building the RAC database.
CFS provides a shared file system which is mounted on all the
cluster nodes simultaneously. When implementing RAC database with
commercial CFS products such as the Veritas CFS or PolyServe Matrix
Server, many different kinds of databases files will be able to be
stored including the shared Oracle Home and CRS Home.
However the capabilities of the
CFS products are not the same. For example, Oracle CFS (OCFS) used
in Linux RAC implementations has limitations. It is not a general
purpose file system. It cannot be used for shared Oracle Home.
Figure 5.5 shows the files locatable on a Cluster File System.
Figure 5.5: Using cluster file
system for shared storage structures
A cluster file system (CFS) is a
file system that may be accessed by all the members in the cluster
at the same time. This implies that all the members of the cluster
have the same view. Some of the popular and widely used cluster file
system products for Oracle RAC include: HP Tru64 CFS, Veritas CFS,
IBM GPFS, Polyserve Matrix Server, and Oracle Cluster File system.
The cluster file system offers:
* Simple management.
* The use of Oracle Managed
Files with RAC.
* A Single Oracle Software
* Auto-extend Enabled on Oracle
* Uniform accessibility of
* ODM compliant File systems.
In these author?s opinions, when
the cluster file system is available for a given platform, it is
preferable to use the CFS rather that the raw partitions. With the
availability of the ODM-compliant cluster file systems, using the
CFS makes much more sense. ODM-based CFS offer similar or even
better performance over raw partitions, and far superior
administrative convenience. The cluster file system set of features
is rapidly advancing. A detailed explanation of the cluster file
system, as well as advances in usage and functionality, will be
offered in later sections of the chapter.
ASM ? Automatic Storage
ASM is the new star on the
block. ASM provides a vertical integration of the file system and
volume manager for Oracle database files. ASM has the capability to
spreads database files across all available storage for optimal
performance and resource utilization. It enables simple and
non-intrusive resource allocation and provides automatic rebalancing
Using ASM for building shared
files would get almost the same performance as that of raw
partitions. The ASM controlled disk devices will be part of ASM
instance which can be shared by the RAC database instance. It is
similar to the situation where raw devices supporting the RAC
database had to be shared by multiple nodes. The shared devices need
to be presented to multiple nodes on the cluster and those devices
will be input to the ASM instance. There will be an ASM instance
supporting each RAC instance on the respective node.
Figure 5.6 shows the files
locatable on the ASM instance and files that have to come out of
Figure 5.6: Using ASM instance
resources for shared storage structures
As shown in the above diagram,
ASM can not provide the generalized storage resources. ASM is for
more Oracle specific data, redo log files, and archived log files.
More detailed explanation of the ASM and its implementation method
is covered in a later part of this chapter.
NFS - Network File System
NFS provides another shared
storage option. Network Appliance Filers offer CFS-like
functionality via NFS to the server machines. These file systems are
mounted using special mount options. RAC database shared data files
can be located on NFS mounts also.
And who is the winner?
From the management and maturity
point, Cluster File System provides an ideal shared storage platform
for all kinds of Oracle related files. Especially with the provision
of Common Oracle Home, the addition of a RAC node and instance
becomes relatively easy. A Large RAC cluster can be built very
easily as Oracle Binaries do not need to be installed for each of
the RAC instance separately. Since a single copy is maintained, it
becomes easy to administer and maintain.
CFS is widely used and many
stable products are available. Such examples include, HP?s Tru64 CFS,
Veritas CFS and PolyServe Matrix Server. The open source product
such as the OCFS (oracle cluster file system) is also widely used in
The cluster file system is the
most reliable and proven method of setting up the storage volumes
into shareable files systems. The ease of use and flexibility of
administration provided by the cluster file system has brought new
interest to the RAC system. The concept, implementation, and various
CFS products available for the RAC database will be examined later
in this chapter.
Using the ASM based shared
storage for RAC database is a recommended method by Oracle. ASM is a
significant new feature in 10g release. ASM removes the management
hassles of raw devices, and provides the performance advantage of
the raw devices. ASM also eliminates the need for cluster file
system. However, ASM is relatively new technology and it does not
provide a general purpose storage platform. ASM offers better
management and tuning of I/O activity. ASM also eliminates the
need for any volume management.
Next, how the physical storage
array is managed and presented to the host will be examined.
Hardware redundancy and design issues will also be explored.