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SQL Server Data Protection
and High Availability
Anil Desai
Speaker Information
• Anil Desai
– Independent consultant (Austin, TX)
– Author of several SQL Server books
– Instructor, “Implementing and Managing SQL
Server 2005” (Keystone Learning)
– Info: http://AnilDesai.net or [email protected]
Overview and Agenda
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Overview of Data Protection and HA
Backup and Recovery
Log-Shipping
Database Mirroring
Database Snapshots
Clustering Overview
Data Protection and HA Goals
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Minimize data loss
Minimize costs
Minimize performance overhead
Simplify implementation and
administration
• Allow fast fail-over
• Implementing transparency for end-users
Implementing Backups
• Features
– Minimal performance hit
– Flexible options
• Purposes
– Protecting against user error
– Protecting against hardware failures
– Disaster Recovery, Security, Archival
– Regulatory Compliance
Planning for Backups
• Backup plan should be based on recovery
requirements
• Factors:
– Type of data / workload
– Acceptable downtime
– Acceptable data loss
– Performance requirements
– Administration overhead (manageability)
Database Recovery Models
• Balances performance vs. recoverability
• Recovery Model Options:
– Full
• All transactions are logged
– Simple
• Does not allow for point-in-time recovery
• Automatic log truncation
– Bulk-Logged
• Bulk operations are not logged
Backup Types
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Full Backups
Differential Backups
Transaction Log Backups
Other Types:
– Copy-Only Backups
– Partial Backups
– File Backups
Restore / Recovery Process
• Restore order:
1. Full backup
2. Latest differential (if any)
3. Chain of transaction log backups
• NO RECOVERY / WITH RECOVERY
Restore / Recovery Example
Restore vs. Recovery
• Restore
– Copies data from backup media
– Applies committed and uncommitted
transactions (“roll forward”)
– Uses NORECOVERY clause (DB = offline)
• Recovery
– Rolls backup uncommitted transactions (“undo”)
– Brings database online
Database Restore Options
• Full database restore
– Point-in-Time recovery / STOPAT Marker
• File restore
• Page-level restore
• Partial / Piece-meal restore (Ent. Ed.)
– Restore read-write filegroups (PARTIAL)
– Bring database online
– Restore read-only filegroups
Backup and Recovery
Commands
• Transact-SQL
– BACKUP DATABASE
– RESTORE DATABASE / RESTORE LOG
• Database Maintenance Plan Wizard
• Copy Database Wizard
• Attach / Detach databases
Backup and Recovery Notes
• Backup history is stored in msdb
• Can use media sets and families
• Security: May need to recreate logins,
certificates, etc.
• Can backup to UNC shares
Log Shipping
• Maintains a “warm” standby server
– Update interval can be configured
– Requires Full or bulk-logged recovery model
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Relies on backup/recovery operations
No special hardware requirements
Can have multiple secondary databases
Roles:
– Primary, Secondary, Monitor
Log Shipping Details
• Continuous restore of transaction logs
• Process:
– Transaction log backup is created on the
primary server
– File is copied to the secondary server
• Log is restored on the secondary server
– NORECOVERY (database remains offline)
– STANDBY (database is read-only)
Implementing Log Shipping
Log Shipping Tool
• Setup from SQL Server Mgmt. Studio:
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Prepare the Primary Database
Implement a Monitoring Server
Initialize the Secondary Database
Copy Files
Security Settings / Proxy Accounts
Can schedule the frequency of backup and recovery
operations
– Create all required jobs
Managing Log Shipping
• Avoid manual backups (except copy-only)
• Log-Shipping information (msdb database)
– Primary Server (backup details)
– Secondary Server (copy and restore details)
– Monitor Server (info about both)
• Transaction Log Shipping Report (SSMS)
Performing a Fail-Over
• Steps for failing-over:
– Disable all log shipping jobs
– Primary Database: Backup and copy transaction log
files (if possible)
– Restore transaction log backups on the secondary
server with NORECOVERY
• Use RECOVERY for last restore
– Re-establish log-shipping (optional)
• Swapping primary and secondary roles
– Can be performed by enabling/disabling jobs
Understanding Database
Mirroring
• Maintains a “hot” standby database
– Synchronization is managed automatically
– Transactions are sent from a Principal to a Mirror
database instance
• Can perform quick fail-over
– Can be automatic or manual
– Clients are automatically redirected
• Works at the database level
– Multiple mirrored pairs per server are possible
Database Server Roles
• Principal Database
– Active, Read/Write database
– Requires the full recovery model
• Mirror Database
– Must be on a separate SQL Server instance
– Set in “Restoring” state
– Can use snapshots to allow read-only access
• Witness (optional)
– Used for establishing a quorum during automatic
failover
– Not recommended for High-Protection mode
Database Mirroring Support
• SQL Server 2005 Standard and Enterprise Ed.
– Witness can be SQL Server 2005 Workgroup or
Express Editions
– For production, should use SP1 or later
• For SQL Server 2005 RTM:
– Must enable Trace flag 1400
– -T1400 startup parameter
– SQL Server Configuration Manager  Advanced
 Startup Parameters
Database Mirroring Modes
• Asynchronous (High Performance)
– Principal transactions commit without waiting for
mirror
– Some transactions may be lost
• Synchronous
– Transactions must be committed at mirror
– Ensures no data loss
– High Protection
• No Witness server / manual fail-over
– High Availability
• Uses a Witness server; automatic fail-over
Implementing Database
Mirroring
• Database Mirror Pairs are independent
– Each set requires own ports
– Can use different modes
– One server can serve as principal, mirror, and
witness for different mirroring pairs
• Steps:
– Back up the Principle database
– Restore the database on the Mirror instance with
NORECOVERY
– Configure Mirroring endpoints and security
– Enable Mirroring
Implementing Database
Mirroring
• Configure Database Mirroring Security
Wizard
– Can include Witness Server
– Configures Mirroring Endpoints
– Service Accounts
• SQL Server Management Studio
– Allows starting, stopping, and fail-over
operations
Database Mirroring Commands
• ALTER DATABASE can be used to administer
database mirroring
• Setting the Mirroring Mode:
– Asynchronous (High Performance):
• SET SAFETY OFF
– Synchronous
• High Availability: SET SAFETY FULL
• High Protection: Use SET WITNESS
• Pausing: SET PARTNER SUSPEND/RESUME
• Cause fail-over: FAILOVER
Forcing a Fail-Over
• Should be used in emergencies
– Use when mirror is out-of-date
– May cause data loss
– If Witness is available, it must be able to
contact the mirror server
• ALTER DATABASE … SET PARTNER
FORCE_SERVICE_ALLOW_DATA_LOSS
Monitoring Database Mirroring
• SQL Server Management Studio
– Database Mirroring Monitor
• System Views / Stored Procedures
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Sys.Database_Mirroring
Sys.Database_Mirroring_Endpoints
Sys.DM_DB_Mirroring_Connections
Sp_DbmMonitorResults
• Other options:
– SQL Server Agent Alerts
– Windows Event Logs
– Windows System Monitor
Database Snapshots
• Snapshots:
– Creates a point-in-time view of a database
– Multiple snapshots can be created
– Quick to create / Requires minimal disk space
– Snapshots are read-only
– Databases can be reverted to a snapshot
– Stored on same instance as database
• Can be accessed like a “regular” database
Understanding Snapshots
• Available in the Enterprise Edition
• Supports all recovery models
• Typical Uses
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Reporting
Point-in-Time Views / Historical Views
Protecting against user error
Testing
• Should not be used as a backup or highavailability solution
• Can be created on a database mirror
Snapshot Architecture
• Initial snapshot creation
– Generates an NTFS Sparse File
– File is initially empty
• Snapshot maintenance
– Monitors for changes to data pages
– Uses copy-on-write method
– Snapshot files will grow based on frequency
of data modification
Creating Database Snapshots
• Creating a new snapshot:
CREATE DATABASE ON
(NAME = LogicalName,
FILENAME = PhysicalFilePath)
AS SNAPSHOT OF SourceDatabase
• Recommendations:
– Use a consistent naming scheme
– Treat snapshots like read-only databases
Managing Snapshots
• Dropping snapshots
– Deletes sparse files
– DROP DATABASE SnapshotName
• Reverting to a snapshot
– Restores a database to the time of the snapshot
– Snapshot and primary database will go offline
– RESTORE DATABASE DatabaseName FROM
DATABASE_SNAPSHOT = SnapshotName
Monitoring Snapshots
• SQL Server Management Studio
– Databases  Database Snapshots
• System Databases
– Sys.Databases
– Sys.Database_Files
– Sys.Master_Files
• Viewing File Details
– Windows Explorer / DIR command
• File size vs. “Size on Disk”
– fn_VirtualFileStats
Clustering Overview
• SQL Server Fail-Over Clusters:
– Provides automatic fail-over
– Multiple nodes that work as a logical unit
– Uses a shared-disk configuration
• Does not protect against disk failures
• Requirements
– Enterprise Ed. and specialized hardware
– Distance limitations
• More difficult to implement and administer
Data Protection and HA Summary
• Backup and Restore
– Standard data protection
• Log-Shipping
– Harder to implement, but more flexible
– Manual fail-over
• Database Mirroring
– Easy to implement and manage
– Automatic fail-over
• Clustering
– Custom hardware requirements
For More Information
• Resources from Anil Desai
– Web Site (http://AnilDesai.net)
– E-Mail: [email protected]
– Keystone Learning Course: “Microsoft
SQL Server 2005: Implementation and
Maintenance (Exam 70-431)”
– The Rational Guide to Managing
Microsoft Virtual Server 2005
– The Rational Guide to Scripting
Microsoft Virtual Server 2005