Disaster Recovery in SQL Server

Rajib Kunduhttp://www.Citagus.com

Agenda

DefinitionsFailover ClusterDatabase SnapshotsLog shippingDatabase Mirroring

Definitions

“Disaster recovery planning is the work that is devoted to preparing all the actions that must occur in response to a disaster. The planning includes the selection of a strategy to help recover valuable data. The selection of the appropriate disaster recovery strategy depends on your business requirements.”

Disaster Recovery Comparisons

Prepare a DRP documentInclude every possible information:

System architecture (How the system/application works)How many systems are involved and what their names are.Their IP Addresses, drive information, file locationsSoftware installed, Contact information of DBA’s, or other key people.Know your SLAs and choose appropriate technology.

Prepare a DRP document(cont.)

Include every possible information…Step by step guide on how to recover each of your system based on different disaster scenarios (Including timelines for recovery)Security information, jobs/schedule information, etc.Make it a reminder for self that any system changes should be updated in this guide.Test, test and test!!!

Failover Clustering

Log Shipping

An automated method of maintaining a warm standby serverBased on SQL Server's backup and restore architecture. Uses the transaction log to track changesRelatively low-tech and inexpensive‘Ships' (copies and restores) a production server's transaction logs to a standby server

Log Shipping (Key terms)

Primary Server: Contains your primary database. SQL Server Agent makes periodic transaction log backups to capture changes.

Secondary ServerContain an unrecovered copy of the production database.One standby server can contain standby databases from multiple primary servers.

Log Shipping (Key terms) cont…

Monitor Server (Optional) Monitors the status of the log-shipping jobs on the primary and each standby server.One monitoring server can monitor multiple primary-standby server pairs. Should use a server other than the primary or the standby to detect problems on either server.

Log Shipping

Database MirroringNewly introduced with SQL Server 2005.Maintains a copy of the principal database as a mirror.Transfers log records from principal to mirror server instance.Works with all hardware that supports SQL Server 2005.Automatic client redirection (using .NET 2.0)Can have a third optional server called Witness server for Auto Failover.

Database Mirroring -Synchronous

Commit

Write to local log

Transmit to mirror

Write to remote log

Log

Acknowledge

Committed in log

Constantly redoing on mirror

Acknowledge

DBDB Log

1

2

2

3

4

5

6

7

Database Mirroring Enhancements

Enhancements in SQL 2008Compression of stream data for which at least a 12.5 percent compression ratio can be achieved.Automatic Recovery from Corrupted Pages.Page read-ahead during the undo phase.Improved use of log send buffers.

General Recommendations

Backup your system databases after modifications.Test if backups are restorable.Practice / Test your disaster recovery plans.Documentation is not only for you.Keep dedicated DR Server ready.Use BACKUP CHECKSUM features.Run DBCC CHECKDB regularly.Don’t ignore any runtime errors.