READ ME before using the Veritas Storage Foundation™ 5.1 SP1 for Oracle RAC Administrator's Guide (April 2011)

Table 2 SG SMS Serviceguard Cluster File System for RAC Bundle Component Products (continued)
DescriptionComponent Product
Manages Oracle RAC databases and infrastructure components.Serviceguard
Manage cluster membership and communications between cluster nodes.RAC Extensions
Communication Infrastructure
To understand the communication infrastructure, review the following data flow information and
communication requirements:
Data Flow
The CVM, CFS, ODM, and Oracle Real Application Clusters (RAC) elements reflect the overall
data flow, or data stack, from an instance running on a server to the shared storage. The various
Oracle processes composing an instance—such as DB Writers, Log Writer, Checkpoint, Archiver,
and Server—read and write data to the storage through the I/O stack in the diagram. Oracle
communicates through the ODM interface to CFS, which in turn accesses the storage through the
CVM.
Figure 2 Data Stack
Oracle
RAC
Instance
Oracle
RAC
Instance
LGWR
ARCH
CKPT
DBWR
ODM ODM
CFSCFS
CVM CVM
Redo
Log
Files
Archive
Storage
Data
and
Control
Files
Disk I/O Disk I/O
LGWR
ARCH
CKPT
DBWR
Communication Requirements
End-users on a client system are unaware that they are accessing a database hosted by multiple
instances. The key to performing I/O to a database accessed by multiple instances is communication
between the processes. Each layer or component in the data stack must reliably communicate with
its peer on other nodes to function properly. RAC instances must communicate to coordinate
protection of data blocks in the database. ODM processes must communicate to coordinate data
file protection and access across the cluster. CFS coordinates metadata updates for file systems,
while CVM coordinates the status of logical volumes and maps.
Figure 3 Communication Stack
RAC
ODM
CFS
CVM
SG/SGeRAC Core
GAB LLT
SGORAC Cluster State
Cache Fusion/Lock Mgmt
Data File Management
File System MetaData
Volume Management
RAC
ODM
CFS
CVM
SG/SGeRAC Core
GAB
LLT
10 Introducing Serviceguard Extension for RAC