Veritas Storage Foundation 5.1 SP1 for Oracle RAC Administrator"s Guide (5900-1512, April 2011)

For database files, when ODM is enabled with SmartSync option, Oracle Resilvering
handles recovery of mirrored volumes. For non-database files, this recovery is
optimized using Dirty Region Logging (DRL). The DRL is a map stored in a special
purpose VxVM sub-disk and attached as an additional plex to the mirrored volume.
When a DRL subdisk is created for a shared volume, the length of the sub-disk is
automatically evaluated so as to cater to the number of cluster nodes. If the shared
volume has Fast Mirror Resync (FlashSnap) enabled, the DCO (Data Change Object)
log volume created automatically has DRL embedded in it. In the absence of DRL
or DCO, CVM does a full mirror resynchronization.
Configuration differences with VxVM
CVM configuration differs from VxVM configuration in the following areas:
■ Configuration commands occur on the master node.
■ Disk groups are created (could be private) and imported as shared disk groups.
■ Disk groups are activated per node.
■ Shared disk groups are automatically imported when CVM starts.
Cluster File System (CFS)
CFS enables you to simultaneously mount the same file system on multiple nodes
and is an extension of the industry-standard Veritas File System. Unlike other
file systems which send data through another node to the storage, CFS is a true
SAN file system. All data traffic takes place over the storage area network (SAN),
and only the metadata traverses the cluster interconnect.
In addition to using the SAN fabric for reading and writing data, CFS offers storage
checkpoints and rollback for backup and recovery.
Access to cluster storage in typical SF Oracle RAC configurations use CFS. Raw
access to CVM volumes is also possible but not part of a common configuration.
For detailed information, see the Veritas Storage Foundation Cluster File System
Administrator's Guide.
CFS architecture
SF Oracle RAC uses CFS to manage a file system in a large database environment.
Since CFS is an extension of VxFS, it operates in a similar fashion and caches
metadata and data in memory (typically called buffer cache or vnode cache). CFS
uses a distributed locking mechanism called Global Lock Manager (GLM) to ensure
all nodes have a consistent view of the file system. GLM provides metadata and
cache coherency across multiple nodes by coordinating access to file system
Overview of Veritas Storage Foundation for Oracle RAC
Component products and processes of SF Oracle RAC
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