RAC and ASM

What is RAC?

RAC stands for Real Application cluster. It is a clustering solution from Oracle

Corporation that ensures high availability of databases by providing instance failover,media failover features.

Benifits of using RAC 

High availability(if one node down, db wont goes down) scalability(adding more nodes as you need) 

Oracle RAC is composed of two or more database instances. They are composed of

Memory structures and background processes same as the single instance database.Oracle

RAC instances use two processes GES(Global Enqueue Service), GCS(Global Cache

Service) that enable cache fusion.Oracle RAC instances are composed of following

background processes:

ACMS—Atomic Controlfile to Memory Service (ACMS)

GTX0-j—Global Transaction Process

LMON—Global Enqueue Service Monitor

LMD—Global Enqueue Service Daemon

LMS—Global Cache Service Process

LCK0—Instance Enqueue Process

What Is Oracle Data Guard?

Oracle Data Guard is a management, monitoring and automation software infrastructure that

works with a production database and one or more standby databases to protect your data against

failures, errors, and corruptions that might otherwise destroy your database. It protects critical

data by providing facilities to automate the creation, management, and monitoring of the

databases and other components in a Data Guard configuration. It automates the process of

maintaining a copy of an Oracle production database (called a standby database) that can be

used if the production database is taken offline for routine maintenance or becomes damaged.

Introduction  to ASM  

In summary ASM provides the following functionality:

Asm is an Integrated file system and volume manager with in the RDBMS kernal, 

The main use of asm is stripping and mirroring.

Manages groups of disks, called disk groups. 

Manages disk redundancy within a disk group. 

Provides near-optimal I/O balancing without any manual tuning. 

Enables management of database objects without specifying mount points and filenames. 

Supports large files.