Hướng dẫn học Microsoft SQL Server 2008 part 112 doc

Nielsen c46.tex V4 - 07/21/2009 3:17pm Page 1072 Part VI Enterprise Data Management ■ The switch between primary and warm standby server is not transparent. A series of steps must be manually executed by the DBA on the warm standby server, and front-end appli- cation connections must redirect the data source and reconnect to the warm standby server. ■ Once the primary server is repaired, returning to the original configuration may require manual DBA intervention. If these issues are acceptable, log shipping to a warm standby server can be an excellent safeguard against downtime. Best Practice I deally, the primary server and the warm standby server should be in different locations so that a disaster in one location will not affect the other. In addition, log shipping can place a large demand on a network every few minutes while the transaction logs are being moved. If the two servers can be connected with a private high-speed network, log shipping can take place without affecting other network users and the bandwidth they require. Defining Log Shipping In SQL Server 2000, log shipping was available only in Developer and Enterprise Editions. Starting with SQL Server 2005, log shipping is available in Workgroup, Standard, Developer, and Enterprise Editions. Developer Edition can be used only for development purposes and not for production. Microsoft provides a simple-to-use log shipping wizard to create a maintenance plan to back up, copy, and restore the transaction log from the primary server to the warm standby server every few minutes. Log shipping has built-in monitoring that makes it very easy to maintain and troubleshoot. Log shipping normally involves three SQL Servers: a primary server, a warm standby server, and a mon- itor server, as shown in Figure 46-1. ■ The primary or source server is the main production SQL Server to which clients connect. This server contains the log shipping database. The initial full database backup and subsequent transaction log backups are taken on this server. This server should be a high-quality server with redundant disk drives. ■ The warm standby server is the backup SQL Server, otherwise known as the secondary server.If the source server fails, it becomes the primary server. This server should be capable of meeting the minimum performance requirements during a short-term crisis. If your business does not allow any performance degradation, then the warm standby server should be similar to the primary server. 1072 www.getcoolebook.com Nielsen c46.tex V4 - 07/21/2009 3:17pm Page 1073 Log Shipping 46 FIGURE 46-1 Typical log shipping configuration Monitor Server Primary Server Warm Standby Server Backup Transaction Log Copy Transaction Log Backup Restore Transaction Log ■ The monitor server polls both the primary server and the warm standby server by keeping track of what files have been sent where, generating an alert when the two are out of sync. A single monitor server can monitor multiple log shipping configurations. The monitor server is optional. If a monitor server is not used, the primary and warm standby servers store the monitoring information. Best Practice T he monitor server can be an instance on the destination server, but locating the monitor server on the source server would be a self-defeating plan. If the source server physically failed, the monitor server would also fail. The best practice is to assign a monitor server to its own hardware to avoid disrupting monitoring in the event that the primary or warm standby server is lost. Each primary server database can have only one log shipping plan, and each plan can ship only one database. However, a plan may ship to multiple secondary servers. 1073 www.getcoolebook.com Nielsen c46.tex V4 - 07/21/2009 3:17pm Page 1074 Part VI Enterprise Data Management Configuring log shipping Log shipping can be configured using one of two methods: either by using SQL Server Management Stu- dio or by using system stored procedures. Pre-log shipping configuration With either method of configuration, the following prerequisites need to be completed before configur- ing log shipping: ■ Disk space needs to be created and shared. This network share is used by the backup job on the primary server to store the transaction log backups. Grant read and write permissions on the network share to the SQL Server service account on the primary server, and read permis- sions to the proxy account for the copy job (usually the SQL Server Agent service account) on the secondary server. ■ The destination folder needs to be created on the secondary servers. The copy job on the secondary server copies the transaction log backups from the network share to the destination folder on the secondary server. The load job then restores these transaction log backups from the destination folder. The SQL Server service accounts on the secondary server need to have read and write permissions on this folder. ■ The recovery model of the log shipping database must be set to full or bulk-logged. ■ The edition of the SQL Server 2008 participating in log shipping needs to be Enterprise, Standard, or Workgroup Edition. ■ If the primary and secondary servers are on different domains, then set up two-way trusts between the domains. If this is not possible, you can also use network pass-through security. With network pass-through security, the SQL Service accounts for all the SQL Servers partic- ipating in log shipping use the same network account and the same password, and enough permission to complete the log shipping tasks. ■ If you have a very large database, then I recommend taking a full database backup, copying it to the secondary server, and restoring it on the secondary server with NORECOVERY or STANDBY to put it into a state that will allow restoring the transaction logs. NORECOVERY mode will not allow any database access to the secondary database, whereas STANDBY mode allows read-only access to the secondary database. Configuring log shipping using Management Studio The following steps create a log shipping configuration using SQL Server Management Studio: 1. In the Object Explorer on the primary server in SQL Server Management Studio, right-click on the database that will be log shipped and review the database properties. 2. On the Options page, verify that the recovery model is either Full or Bulk-logged and not Simple. 3. On the Transaction Log Shipping page, shown in Figure 46-2, check the box that enables log shipping configuration. 1074 www.getcoolebook.com Nielsen c46.tex V4 - 07/21/2009 3:17pm Page 1075 Log Shipping 46 FIGURE 46-2 Enabling the primary database for log shipping 4. Configure the backup settings as shown in Figure 46-3 by clicking the Backup Settings button. Enter the network share where the transaction log backups will be stored before being copied to the secondary server. If the backup folder is local to the primary server, then enter the local folder path too. A network share that is not located on the primary server will better protect the transac- tion logs in case of a hardware failure on the primary server. 5. Enter an amount of time after which the transaction log backup files should be deleted. For example, if the files should be deleted after one day, then the ‘‘Delete files older than’’ option should be set to one day. 1075 www.getcoolebook.com Nielsen c46.tex V4 - 07/21/2009 3:17pm Page 1076 Part VI Enterprise Data Management FIGURE 46-3 Configuring transaction log backup settings for log shipping 6. Enter an amount of time that the server should wait to send an alert if no new transac- tion log files are found. For example, if the server has not seen a transaction log backup in the past one hour, then the ‘‘Alert if no backup occurs within’’ option should be set to one hour. The longer the length of the alert time, the higher the risk. With a long alert setting, a transaction log backup failure will result in a larger amount of data loss. 7. Schedule the job that will back up the transaction log by setting the job’s name, time, and frequency by clicking the Schedule button. A shorter duration between transaction log backups will minimize the amount of data that could be lost. By default, the transaction log is backed 1076 www.getcoolebook.com Nielsen c46.tex V4 - 07/21/2009 3:17pm Page 1077 Log Shipping 46 up every 15 minutes. The default works for most environments but some of my clients have changed it to 5 minutes to minimize data loss. The frequency of transaction log backups usually is determined by several factors, including service-level agreements, speed of your disk subsystem, and transaction log size. Make sure that the only transaction log backup that occurs is scheduled through the Trans- action Log Shipping page. Otherwise, all the data changes will not be propagated to the secondary servers and log shipping will break. If you have a very powerful server with plenty of resources, you may be tempted to change the transaction log backup frequency to every 1 minute or less. SQL Server 2008 lets you schedule the frequency to every 10 seconds. While it is possible that you may need this in your environment, remember that this creates hundreds of transaction log backups. If you have to restore your database using backups, then you will have to restore the full database backup followed by all the transaction log backups in order; and if one of the transaction log backups is bad, then the restore will stop at that point. 8. SQL Server 2008 Enterprise Edition supports backup compression. You can control the backup compression by clicking the ‘‘Set backup compression’’ drop-down box on the Trans- action Log Backup Settings page. By default, ‘‘Use the default server setting’’ option is selected. This uses the default server-level compression. You can bypass the server-level default by selecting the ‘‘Compress Backup’’ option or you can choose not to compress the backup by selecting the ‘‘Do not compress backup’’ option. The performance increase achieved from backup compression comes at the expense of CPU usage. If you have a CPU-bound SQL Server, then you may not want to compress the backup. Thorough testing is recommended to determine the impact of the backup compression, as the CPU increase can impact other operations. 9. Add the secondary servers to the transaction log configuration by clicking the Add button under the secondary instance’s window. Multiple secondary instances can be added here by repeating steps 9 through 16. 10. On the Secondary Database Settings screen, shown in Figure 46-4, connect to the server that will be the secondary server and enter the database name for the secondary database. If the database is not there it will be created. 11. Initialize the secondary database by selecting either the option to have log shipping cre- ate a full database backup and restore it on the secondary server or the option to have it use the last known backup. If you select to use the last backup that was created, the name of the directory in which the backup is located needs to be supplied. To create the data and log files on non-default folder locations on the secondary server, click the but- ton ‘‘Restore Options’’ and enter the local folder path on the secondary server where you want the data and log files to exist. The previous two options are best suited for smaller databases. If you have a very large database, it is recommended that you bypass the wiz- ard and manually take a backup of the database, copying it to the secondary database and restoring it. If you take this approach, select the third option, ‘‘No, the secondary database is initialized.’’ 1077 www.getcoolebook.com Nielsen c46.tex V4 - 07/21/2009 3:17pm Page 1078 Part VI Enterprise Data Management FIGURE 46-4 Configuring the secondary server database for log shipping 12. The Copy Files tab, shown in Figure 46-5, configures the copy job on the secondary server that copies the transaction log backups from the network share to the destination local folder on the secondary server. This tab also has a setting that enables files to be deleted after a designated amount of time. 13. On the Copy Files tab, enter the local folder on the secondary server to which the transaction log files will be copied. The proxy account for the copy job (usually the SQL Server Agent service) on the secondary server must have read and write permissions on this folder. 14. On the Restore Transaction Log tab, shown in Figure 46-6, choose either No recovery mode or Standby mode. Standby mode allows access to the secondary server for read-only operations. Select this mode if you want to use log shipping for reporting. If the standby mode is selected, the option to have the user connection killed during the transaction log restore is available. If you do not choose to disconnect the users, the transaction log backups will fail and the secondary server will lag behind. The No recovery mode option will not allow any database access to the secondary database. This option is usually selected when log shipping is used for disaster recovery or high-availability scenarios. 1078 www.getcoolebook.com Nielsen c46.tex V4 - 07/21/2009 3:17pm Page 1079 Log Shipping 46 FIGURE 46-5 Configuring the copy job on the secondary server To use log shipping as a reporting solution you need to select Standby mode in the Restore Transaction Log tab. The restore job needs exclusive access to the database and will fail if users are running reports. You may select the option to disconnect the users in the database when restore runs, but this means that longer-running reports may never complete. For example, if you have a restore job that runs every 15 minutes and you have a report that takes 25 minutes to complete, that report will always be killed by log shipping every 15 minutes. Conversely, you may configure the restore job to occur every few hours, but in that case the secondary server will lag behind the primary server. Because log shipping allows multiple secondary servers, you may have two secondary servers. Set one to no recovery mode and schedule the restore job to run every 15 minutes or earlier, and set the recovery mode to standby mode on the second secondary server. Then, schedule the restore job to run every few hours. This way you will have two copies of your primary database and can use log shipping for a high-availability and reporting solution. If near real-time data is required for reporting, I recommend using transactional replication. 1079 www.getcoolebook.com Nielsen c46.tex V4 - 07/21/2009 3:17pm Page 1080 Part VI Enterprise Data Management FIGURE 46-6 Configuring the restore transaction l og job on the secondary server 15. On the Restore Transaction Log tab, the option for delaying a restore and alerting is avail- able as well. This configuration option enables all the transaction log backups to be held until the end of the business day or to apply the transaction logs as soon as they are received. 16. The option for more granularities on restores and when they are applied are set in the Restore job by clicking the Schedule button. By default, transaction log backups are restored every 15 minutes on the secondary server. 17. Click OK to complete the secondary database setup, and return to the database’s Properties tab. 1080 www.getcoolebook.com Nielsen c46.tex V4 - 07/21/2009 3:17pm Page 1081 Log Shipping 46 18. Once the secondary database configuration has been completed, a monitor server can be con- figured on the primary database’s Properties page by checking ‘‘Use a monitor server instance’’ and clicking the Settings button as shown in Figure 46-7. As noted previously, adding a monitor server is optional. But if you do not add a monitor server now you cannot add it later. And if you add a monitor server now, it cannot be changed without removing log shipping first. FIGURE 46-7 Configuring the monitor server for log shipping 1081 www.getcoolebook.com . this server. This server should be a high-quality server with redundant disk drives. ■ The warm standby server is the backup SQL Server, otherwise known as the secondary server. If the source server. primary server, a warm standby server, and a mon- itor server, as shown in Figure 46-1. ■ The primary or source server is the main production SQL Server to which clients connect. This server contains. Server Primary Server Warm Standby Server Backup Transaction Log Copy Transaction Log Backup Restore Transaction Log ■ The monitor server polls both the primary server and the warm standby server