Day 2 : Architecture and Concepts Part I

 

RAC Requirements

Nodes:

The nodes are one of the major components where the Oracle instance resides. This is the place where data-actual database processing takes place.

Interconnect:

The cluster interconnect is a high bandwidth (preferably 1gigabit or more), low latency communication facility that connects each node to other nodes in the cluster and routes messages among the nodes.

In general, the clusters interconnect is used for the following high-level functions:

Monitoring health, Status, and Synchronous messages
Transporting Distributed lock manager (DML) messages
Accessing remote file systems
Moving application-specific traffic
Providing cluster alias routing

It is a communication path used by the cluster for the synchronization of resources and is also used in some cases for the transfer of data (cache fusion) from one instance to another instance. Typically, interconnect is a network connection is dedicated to the server nodes of a cluster (and thus sometimes refer to as a private interconnect) and has a high bandwidth and low latency.

Shared Storage System:

DAS – Directly Attached Storage

Direct-attached storage (DAS) refers to a digital storage system directly attached to a server or workstation, without a storage network in between.

The main protocols used for DAS connections are ATA, SATA, eSATA[1], SCSI, SAS, and Fibre Channel.

NAS – Network Attached Storage

Network-attached storage (NAS) is file-level computer data storage connected to a computer network providing data access to heterogeneous clients.

The main protocols used for NAS connections are CIFS, NFS, FTP,SFTP, HTTP and rsync

SAN – Storage Attached Network

A storage area network (SAN) is a dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally attached devices to the operating system.

The main protocols used for SAN connections are ATA, SCSI and Fibre Channel.

RAC Cluster components:

1. Clusterware
2. RAC Shared Disk Components
3. RAC specific Daemon and Instance Processes
4. Global Cache services and Global Enqueue services.

Clusterware

a. OSD Clusterware
b. Oracle Clusterware

OSD Clusterware

The clusterware contains operating system-dependent (OSD) components that control the operating system and clusterware. The OSD’s two primary subcomponents are the Cluster Manager (CM) and the Interprocess Communication (IPC) software

Components of OSD Clusterware are:
Cluster Manager
Node monitor
Interconnect

Cluster Manager:

Cluster Manager is responsible to group the individual servers into single component. it informs the client and oracle server when the status of cluster resource change.

Node monitor:

Node monitor is responsible for monitering the nodes.

Interconnect:

This is used to connect one node to another node to transfer data.

Different Types of Clusterware are:

PLATFORM	CLUSTERWARE
Solaris	Sun Cluster 3.1
Solaris	Veritas Storage Foundation DBE/AC
Solaris	Fujitsu-Siemens PrimeCluster
HP UX	MC Service Guard and Veritas Storage Foundation
HP Tru64	Tru64 TruCluster
Linux	Oracle Supplied Clusterware (CRS)
Windows	Oracle Supplied Clusterware (CRS)
AIX pSeries	HACMP

Oracle Clusterware

1) Cluster Ready Services (CRS)
2) Cluster Synchronization Services (CSS)
3) Event Management (EVM)
4) Oracle Notification Service (ONS)
5) Process Monitor Daemon (OPROCD)

1) Cluster Ready Services (CRS)

Cluster Ready Services(CRS) is a high availability framework for managing any application that runs on your cluster. CRS manages applications to ensure they start when the system starts. CRS also monitors the applications to make sure that they are always available. any thing that CRS manages is known as Cluster Resources for example: database, instances, vip, services and listeners etc .CRS manages the cluster resources based on the resource configration information that is stored in oracle Cluster registry(OCR).
If a failure occurs, Cluster Ready Services automatically attempts to restart the failed component and also redirects operations to a surviving component.
NOTE:- CRS by default attempts 3 times for ONS, once for database and 5 times for other components.

CRS includes two important components:
1). Oracle Cluster Registry (OCR) :- the OCR is a file that manages the RAC database configuration information and Cluster Resources information
2). Voting disk :- The voting disk is a file that manages information about node membership.

2) Cluster Synchronization Services (CSS)

An Oracle Clusterware component that discovers and tracks the membership state of each node by providing a common view of membership across the cluster. CSS also monitors process health, specifically the health of the database instance.
Oracle Cluster Synchronization Services Daemon (ocssd) provides synchronization services between nodes. It also enables basic cluster services including cluster group services and cluster locking. This is also required in a single instance configuration if Automatic Storage Management (ASM) is used.

3) Event Management (EVM)

The background process that publishes Oracle Clusterware events and event management logger. It monitors the message flow between the nodes and logs the relevant event information to the log files.

4) Oracle Notification Service (ONS)

A publish and subscribe service for communicating information about all FAN events.

5) Process Monitor Daemon (OPROCD)

This process insures that nodes that are no longer part of the cluster can no longer initiate any I/O. This process is called I/O fencing. For example, if a node initiated a write to a database and then froze for some reason before the write was completed the node could be ejected from the cluster. If, after  being ejected from the cluster the node was suddenly freed from its frozen state and the write that it had initiated suddenly tried to complete it could corrupt data. Having I/O Fencing in place prevents this from happening. This process must also be run as the root user.

cont……………

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