SQL Server Clustering Part1

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Clustering SQL Server

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ByKareem Syedwww.optimizesql.blogspot.in

Agenda

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• Understanding Windows Clustering• Working with SQL Clustering• Monitoring Clustering• Troubleshooting Clustering


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SQL Server High Availability Goal of High Availability is to keep systems, applications, email,

databases etc always running

HA Overview


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Server downtime is unavoidable. But we have to keep the business running and competitive. Server may go offline due to

Maintenance Upgrade

Software or Hardware Updates

Hot fixes, security patches Accidently Power Outages Disasters

Importance of HA


Group of two or more servers (Nodes) that work together and represent themselves as single Server (Virtual Server) in the network.

A server cluster is a collection of servers, called nodes that communicate with each other to make a set of services highly available to clients.

Server clusters are designed for applications that have long running in-memory state or frequently updated data.

Introduction to Clustering


Introduction

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• A Microsoft SQL Server Cluster is simply a collection of two or more physical servers.• These Servers are called Nodes.• These nodes have same access to shared storage and provides the resources required to store the database files• Each of the nodes talk to one another via a network• If one node does not communicate to the other node the other

node will take ownership of SQL Server service. This process is called fail over.• A failover can occur both automatically (a server stops communication for some reason) or manually.


Client PCs

Server A Server B

Shared

Disk Array

HeartbeatCluster management

SQL Server

Virtual Server

E F GC,D C,D

SQL Server

Hub Hub

Basic Architecture


BinnInstallUpgrade

BinnInstallUpgrade

BackupDataFTDataJob, Log, repldata

Client PCs

Server A Server B

Shared

Disk Array

HeartbeatCluster management

SQL Server

Virtual Server

E F GC,D C,D

Hub Hub

SQL Server

Basic Architecture


Feature Database Mirroring

Failover Clustering

Log Shipping

Data Loss No data loss option

No data loss Maybe

Failover Automatic failover option

Automatic failover No

Failover time seconds ~ 20+ seconds Manual

Special Hardware

No Certified hardware No

Redundancy Complete redundancy

Disks are shared Complete redundancy

Multiple Secondaries

No No Yes

Standby Read Access

Yes, through snapshot

No Yes, WITH STANDBY option

Granularity Database Instance Database

Conn String Two ONE Two

Importance of HA


Advantages

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• High Availability• Protection from failures

• Server level – hardware and software failures, service failures etc

• Site level – Fires, earthquake etc• Online Administration

• Software/hardware upgrades/patch and restart with minimal downtime.

• Increased Scalability• In some cases, clustering can be used to increase the

scalability of an application. For example, if a current cluster is getting too busy, another server could be added to the cluster to expand the resources and help boost the performance of the application.• Clustering is transparent to the calling application.


Advantages

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• Manageability• Enables managing resources within entire cluster if we are

managing a single computer.• Instance level redundancy and automatic failover for SQL Server


Advantages

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• Reduces downtime.• Allows for an automatic response to a failure in hardware/

software.• Allows you to perform upgrades without forcing users off the

system for extended periods of time.• Clustering doesn’t require any servers to be renamed. So when failover occurs, it is relatively transparent to end-users.• Failing back is relatively quick, and can be done whenever the

primary server is fixed and put back on-line.• In some cases, clustering can be used to increase the scalability of an application. For example, if a current cluster is getting too busy, another server could be added to the cluster to expand the resources and help boost the performance of the application• Clustering is transparent to the calling application.www.optimizesql.com/blog SQLDBA

Disadvantages

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• Failover Cluster is NOT designed to:• Protect data• Protect against a shared disk array from failing.• Load Balance• Prevent server from potential data disasters.

• Requires more on-going maintenance than other alternatives.• Requires more experienced DBAs and network administrators.


Disadvantages

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• This can be expensive.• Requires more set up time than other alternatives.• Requires more on-going maintenance than other alternatives.• Requires more experienced DBAs and network administrators.



What SQL Server services can we cluster?

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• Clusterable• SQL Server• SQL Server Agent• Analysis Services

• Non Clusterable• SQL Server Integration Services• SQL Server Reporting Services• SQL Browser• SQL Writer

• Full – text search (FTS) service? • From SQL Server 2008, FTS service is integrated into SQL Server

engine


Active and Passive

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• SQL Server offers Single Instance Clusters and Multi-Instance

Clusters.

Single InstanceOnly one SQL Server Instance running at any given time on your cluster. It’ll be running either on your 1st node or 2nd node.(Active-Passive).

Multi Instance We have 2 nodes running 2 Instances or even 4 Instances of SQL Server, Or let’s say you’ve 3 nodes where you’ve 2 Instances of SQL Server(Active-Active-Passive), the third node serving as a standby node ready to take ownership in an event of any failure of Node1 or Node2.

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Basic Architecture


Node1Active SQL

Instance1

Node2Passive

Virtual Name

Public Network

SANShared Storage

Private Network

Heart Beat

Active/Passive Cluster


Basic Architecture


Node1Active SQL

Instance1

Node2ActiveSQL

Instance2

Virtual Name

Public Network

SANShared Storage

Private Network

Heart Beat

Active/Active Cluster


Basic Components

A minimum of two identical servers. Two NICs are needed per server.

Private, Public Storage (optional)

Shared disk storage (SAN) Quorum – (Maintains cluster meta data) – 256MB MSDTC – (Replication/Dist Trans) SQL Server (Backup,FTData,data,repldata,log,job) Tempdb Data, T.Log Files

Distributed Transaction Coordinator (DTC)

Operating System, service or Application


Domain Controller.


Failover Clustering Terminology

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• SQL Server virtual server

• It is cluster-configured resource group that contains all resources necessary for SQL Server to operate on the cluster. This includes

• NetBIOS• Name of the virtual server, • TCP/IP address for the virtual server• All disk drives, • SQL Server services



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• Heartbeat

• A single User Datagram Protocol (UDP) packet is sent every 500 milliseconds between nodes in the cluster across the internal private network,

• This packet relays health information about the cluster nodes as well as health information about the clustered application



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• Failover

• It is the process of one node in the cluster changing states from offline to online.

• It results in the node taking over responsibility of the SQL Server virtual server.

• The Cluster Service fails over a group in the event that node becomes unavailable or one of the resources in the group fails.



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• Failback

• Failback is the process of moving a SQL Server virtual server that failed over in the cluster back to the original online node.



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• Quorum Resource

• The quorum resource, also referred to as the witness disk in Windows Server 2008.

• It is the shared disk that holds the cluster server’s configuration information.

• All servers must be able to contact the quorum resource to become part of a SQL Server 2008 cluster



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• Resource Group

• A collection of cluster resources such as the SQL Server NetBIOS name, TCP/IP address, and the services belonging to the SQL Server cluster.

• A resource group also defines the items that fail over to surviving nodes during failover.

• Resource group is owned by only one node in the cluster at a time.



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• LUNs

• An LUN is used to identify a disk or a disk volume that is presented to a host server or multiple hosts by the shared storage device.


Preparing Windows Clustering

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• Pre installation checklist

• Ensure that all nodes are working properly and are configured properly.• Confirm that each node can access shared array or SAN drives.• Verify that none of the nodes have been configured as domain controller.• Verify that all drives are NTFS and are not compressed.• Ensure that private and public networks are properly configured.• Verify that you have disabled NetBIOS for all private network cards.• Verify that Windows Task Scheduler service is running on each node.• Take a domain admin account for configuring windows cluster.• Use separate account for cluster service.• Add cluster service account to the Local Administrators group of all the

nodes in the cluster.• Decide windows cluster virtual name and virtual IP.



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• Pre installation checklist

• Ensure that shared drives are available for the following requirements

• Quorum• MSDTC• TempDB• User Defined database data files• User Defined database T.Log files• Backups



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• IP Address Requirements

Name of Resource IP Address

Private Network – heartbeat (one per node) 2

Public Network (one per node) 2

MSDTC 1

Windows Cluster Name 1

SQL Cluster Name 1