Download Disaster Recovery with SQL Server

Vinod Kumar
Technology Evangelist | Microsoft
http://www.ExtremeExperts.com
http://bogs.sqlxml.org/vinodkumar
Agenda
Definitions
Disaster Recovery Planning
Database Snapshots
Log shipping
Database Mirroring
What to do when system databases crash
Rebuilding System Databases
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Definitions
For clarity, we’ll use the following definitions
today:
Disaster: an event that results in serious loss of data
or service
Disaster Recovery: A process that allows
continuation of business following a disaster, including
manual methods
Offsite Disaster Recovery: A process that allows
disaster recovery at a remote location (usually entire
site)
Business Continuity: A process that includes
disaster recovery and offsite disaster recovery as well
as using systems to avert disasters, such as faulttolerant hardware and software
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Definitions
As per http://support.microsoft.com/kb/822400/en-us
“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.”
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Type of disasters
Natural Disasters:
Tsunami, Katrina,
Rita, etc
Fire
Power outage/failure
Organized
disruptions
Theft
System failures
Legal issues
Wars
Strikes
Human error
Viruses, etc.
Disaster Recovery Drivers
Symantec Annual IT Survey Results
Others
18%
IT Problem
10%
Data Leakage or Loss
8%
Employee Error
10%
Hardware/Software
Failure
20%
External Security
Threats
12%
Natural Disasters
12%
Power Outages
10%
Hardware/Software Failure
External Security Threats
Natural Disasters
Power Outages
Employee Error
Data Leakage or Loss
IT Problem
Others
Published in IT News 9/9/2008 – Symantec Annual IT Survey
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Prepare a DRP document
Include 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
locations
Software installed, Contact information of
DBA’s, or other key people.
Know your SLAs and choose appropriate
technology.
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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)
Make sure you discuss DRP guide with all the
parties involved.
Security information, jobs/schedule
information, etc.
Make it a reminder for yourself that any system
changes should be updated in this guide.
Test, test and test!!!
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Database Snapshots
Read-only, consistent view
of a database
Page
Specified point-in-time
Modifying data
Copy-on-write of affected
pages
Reading data
Accesses snapshot if data
has changed
Redirected to original
database otherwise
Page
12:00 Snapshot
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Database snapshot
1. Recovering modified data
2. Recovering dropped object
3. Restoring from Snapshot
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Log Shipping
An automated method of maintaining a
warm standby server
Based on SQL Server's backup and restore
architecture. Uses the transaction log to
track changes
Relatively low-tech and inexpensive
‘Ships' (copies and restores) a production
server's transaction logs to a standby server
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Log Shipping (Key terms)
Primary Server:
Contains your primary database.
SQL Server Agent makes periodic transaction
log backups to capture changes.
Secondary Server
Contain an unrecovered copy of the production
database.
One standby server can contain standby
databases from multiple primary servers.
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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.
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Log Shipping
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Database Mirroring
Newly 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.
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Database Mirroring -Synchronous
Commit
1
Acknowledge
Acknowledge
7
6
Constantly
redoing on mirror
2
Write to
local log
Transmit to mirror
2
3
DB
Log
Committed
in log
4
Write to
remote log
5
Log
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DB
Database Mirroring Enhancements
Enhancements in SQL 2008
Compression 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.
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Database Mirroring
Automatic Failover
Auto page repair (SQL 2008)
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Rebuilding System Databases
SQL 2000
Use RebuildM.exe (UI based)
Need setup media for Database files
SQL 2005
Use Setup.exe (Command Prompt based)
Need setup media for setup.exe and database files.
SQL 2008
Use Setup.exe (Command Prompt based)
Setup media not required. Files copied during initial
installation.
Will not Rebuild Resource database.
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Rebuilding System Databases
Setup.exe file located under %Program
Files%\Microsoft SQL Server\100\Setup
Bootstrap\Release
Database Files used by setup are located
under %Program Files%\Microsoft SQL
Server\MSSQL10.<INSTANCENAME>\MSS
QL\Binn\Templates
Files Missing?
Copy from setup media
Apply service packs/patches after rebuilding
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System databases disaster
Master database loss
SQL Server won’t start
Rebuild system databases
Start SQL in single user mode and restore master
Msdb database loss
SQL Agent won’t start.
Restore msdb
Model database loss
SQL Server won’t start.
Rebuild system databases
Restore master, msdb and model
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Best Practices
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.
Summary
Murphy’s Law on Disaster…
If there is a possibility of several things going
wrong, the one that will cause the most
damage will be the one to go wrong.
If you fail to plan, you are planning to fail.
Off-site backups always help.
Auto page repair is a band-aid.
References
SQL Server Books online
http://msdn.microsoft.com/en-us/sqlserver/default.aspx
Planning for SQL Disaster Recovery
http://technet.microsoft.com/en-us/library/ms178094.aspx
Database Mirroring Whitepaper
http://www.microsoft.com/technet/prodtechnol/sql/2005/db
mirror.mspx
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