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Figure 1-5
Using Database Snapshot to make point-in-time copies of a database
Backup and Restore A sound backup and recovery plan is an essential component to high availability SQL Server database backups can be performed to disk, tape, or to other media Without a doubt, disk-based backups are the fastest mechanism for backing up and restoring data However, to protect against drive failure, backups should always be directed to a separate drive and preferably to a separate system from your database server SQL Server supports three types of database backup: full, differential, and transaction log backups, as follows: Full backup A full database backup is a complete copy of the database Full backups provide a known point from which to begin the database restore process Di erential backup A di erential backup copies only the database pages modi ed after the last full database backup Frequent di erential backups minimize the number of transaction log backups that need to be applied to bring your database up to the last current transaction Transaction log backup The transaction log backup copies the changes that have occurred since the last full or di erential backup You can make multiple transaction log backups per day depending on the activity level of your system Transaction log backups may be applied after the last full or di erential backup has been restored SQL Server s backup and restore process allows an entire database to be recovered to any given point in time For example, if an application error occurred at 03:00 that resulted in a corrupted database, you could restore the database and then use SQL Server s transaction log backup to recover the database to 02:59, which would be just before the point that the data corruption occurred Restoring a database is often a lengthy operation, and depending on the type of failure, a small loss of data can occur
C h a p te r 1 : P l a n n i n g fo r H i g h Ava i l a b i l i t y
Selecting a High Availability Technology Selecting the appropriate high availability technologies requires matching your organization s availability needs and budget to the capabilities and requirements of the different high availability technologies The different technologies provided by SQL Server 2008 are designed to give different levels of availability and data protection They each have different costs as well as hardware and technological skill level requirements Table 1-2 summarizes some of the key availability technology to best fit your organization s requirements
Feature
Very Low Latency Failover Database Clustering Mirroring
No data loss No data loss
Medium Latency Peer-to-Peer Log Transactional Shipping Replication
Some data loss possible No No Some data loss possible No No
High Latency Database Backup/ Snapshots Restore
Some data loss No No Some data loss
Data loss
Automatic failover
Yes Yes
No No
Transparent Yes to client Downtime 20 sec + database recovery time
< 10 seconds
Minutes time to perform manual failover
Minutes time to perform manual failover + database recovery time Intermittently accessible
Minutes time to restore database from snapshot No
Minutes to hours time to restore database from backup media No
Standby data access
Mirror accessible via database snapshot
Protection level
All system and User database user databases (SQL Server instance level) High Medium
Table
User database
User database User database
Complexity Table 1-2
Medium
Medium
Summary of SQL Server 2008 s High Availability Options
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Part # I
Implementing Windows Failover Clustering
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2
Windows Failover Clustering Architecture
In This
Overview Windows Failover Cluster Con gurations Windows Failover Cluster Components New Failover Clustering Features in Windows Server 2008 SQL Server 2008 Failover Clustering Support
M i c ro s o f t S Q L S e r ve r 2 0 0 8 H i g h Ava i l a b i l i t y
indows failover clustering is designed to protect your critical business applications like SQL Server from unplanned downtime In this chapter, you ll get an overview of Windows Server 2008 Failover Clustering Here you ll learn about the architecture and components that comprise a Windows failover cluster, some of the new features in Windows Server 2008 Failover Clustering, and SQL Server 2008 s support for failover clustering
Overview
Windows failover clustering is Microsoft s primary technology for providing high availability at the server level Windows failover clustering essentially involves utilizing multiple servers in a group or cluster If one of the servers in the cluster has a system failure, then one of the other servers in the cluster can take over the workload of a failed server Each physical server in the cluster is called a node, and the nodes work together to form the cluster All of the nodes in a failover cluster constantly communicate If one of the nodes in a cluster becomes unavailable and loses communication with the other nodes in the cluster, another node will automatically assume its duties and begin providing users with the same services as the failed node This process is called failover When the failed node is repaired, services can be restored to the node This process is referred to as a failback Windows failover clustering provides the following features: Automatic failover When a node fails, the cluster automatically switches the services to a backup node Rapid failover In many cases the failover process can complete in less than 30 seconds Transparent to clients After a failover, clients can immediately reconnect to the cluster with no network changes Transactional integrity There is no data loss For SQL Server, all committed transactions are saved and reapplied to the database after the failover process completes The failover process does have some downtime associated with it, but it is a totally automated process When a failover occurs, the Windows failover cluster will restart the failed services or applications on one of the remaining nodes The period required to complete the failover depends in part on the hardware used and in part on the nature of the service or application From a hardware standpoint the clustered services or application must be restarted on the backup node Then the application or service must perform its own startup tasks For a database application like SQL Server, the length of
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