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Oracle Tips by Burleson |
Oracle Disk I/O Tuning
Chapter 5:
Configuration of CFS or Raw Devices
CVM does not attempt to
do any locking between the nodes. That is the responsibility of the
application, as in the RAC database. CVM also follows the ‘uniform
shared storage’ model. This means that all systems must be connected
to the same disk sets for a given disk group. If a node loses
contact with a specific disk, it is excluded from using the disk.
Cluster File System (CFS)
Veritas CFS has evolved
from the Veritas File System (VxFS). CFS allows the same file system
to be simultaneously mounted on multiple nodes in the cluster. Once
again, the CFS is designed with master/slave architecture. Though
any node can initiate an operation to create, delete, or resize
data, the master node carries out the actual operation. CFS caches
the metadata in memory, typically in the memory buffer cache or the
vnode cache. A distributed locking mechanism, called GLM, is used
for metadata and cache coherency among the multiple nodes.
However, with implementation of the ODM
interface, Oracle RAC accesses data files stored on CFS, bypassing
the file system buffer and file system locking processes. Oracle
manages its own consistency mechanism. The ODM facility is
automatically invoked with RAC.
The above text is
an excerpt from:
Oracle Disk I/O Tuning
Disk IO Performance & Optimization for Oracle
Databases
ISBN
0-9745993-4-4
by Mike Ault
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