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SQL Server Disaster RecoveryDetroit Area SQL Server User’s Group

Drew Flint

Plexus Systems Inc.

7/10/08

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Biography

Married to wife Missy for 12 years

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Biography

Eldest Son – Benjamin

6 Years Old

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BiographySon – Ryan 4 Years Old

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BiographyDaughter – Emma 20 Months

Old

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Agenda

• What is a disaster?• Disaster Recovery Terminology (light version)• Software Disaster Recovery Options• Hardware Disaster Recovery Options• SQL Server DR things to know• DR Plan Suggestions

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Disaster

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Disaster

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Disaster

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Disaster

• Webster’s definition: A calamitous event, esp. one occurring suddenly

and causing great loss of life, damage, or hardship, as a flood, airplane crash, or business failure.

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Disaster

• Drew’s definition: Any event that causes your system to not operate

for a prolonged period of time.

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Disaster Recovery Terminology

• Recovery Time Objective – RTO– The amount of time system recovery must occur.

This is usually measured in hours.

• Recovery Point Objective – RPO– The maximum amount of acceptable data loss.

This is usually measured in hours.– http://www.drj.com/glossary/drjglossary.html

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Software Disaster Recovery Options

• General Truths about Software Solutions– They cost less money than hardware based

solutions.– They often require your system to do more work.

Due to their consumption of resources your database server would normally use for day to day processing: • RAM• CPU• Disk

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Software Disaster Recovery Options• SQL Server Replication• SQL Server Database Mirroring• Third Party Solutions

– Replicator X (NetApp) – Example given– GoldenGate Software - http://www.goldengate.com/ – WAN Sync - CA XOSoft - http://www.xosoft.com/ – Double-Take Software - http://www.xosoft.com/ – Steeleye for SQL -

http://www.steeleye.com/products/sqlserver.php

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SQL Server – Trans. ReplicationSQL Server Database

SQL Server Database

Table

Publisher

Subscriber

Table

SQL Server Distribution Database

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Pros of SQL Server Replication

• Very rapid transport of end user data.• It can synchronize most of the common

schema changes.• It’s included in the price of SQL Server

assuming Work Group edition or higher. There is a limit on the number of publications on Work Group Edition (25).

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Cons to SQL Server Replication• Transaction log files will experience growth.

How much depends on:– Frequency of replication– Transaction log backups

• Optimal configuration will require the introduction of an additional database server to function as the remote distributor.

• It increases the complexity of making schema changes to articles included in publications.

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SQL Server Database Mirroring

Partner DB Server Partner DB Server

Witness DB Server

Principal Mirror

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Pros of Database Mirroring• It’s included in SQL Server editions standard

or higher. • The witness server can be a lesser version of

SQL Server, down to Express Edition.• Has many different levels of protection:

– Full (completely automatic failover)– High Protection (manual failover)– High performance (forced only).

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Cons of Database Mirroring• Scenarios where the mirror causes the failover

unnecessarily.• Transaction logs have the potential of growing.

Sometimes significantly should the “mirror” partner server become unavailable for an extended period of time.

• No way to define database consistency groups. It assumes your databases are independent.

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Replicator X

• This is a NetApp solution that can replicate data from any disk that is attached to the database server.

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How Replicator X Works

VRR (RAM)

Bitmap of source volume

RXRCReplication Client

Source Drive

Data

RXRSReplication Server

RXRCReplication Client

SANData

Data

VRR (RAM)

Bitmap of source volume

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Pros of Replicator X

• Extremely flexible. It can address pretty much any storage data migration scenario.

• Small footprint on server. Low CPU/RAM consumption.

• It supports scripting to trigger events.

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Cons of Replicator X

• Very costly solution.• High level of expertise to properly configure

environment. Lots of moving parts to configure correctly for optimal configuration.

• Pay per TB replicated.

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Hardware Disaster Recovery Options

• Recovery Point (EMC) & Unisys 30M• NetApp Snapmirror (SAN Based)• EMC MirrorView (SAN Based)

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Recovery Point/UNISYS 30M

• In order to replicate data, both solutions use the combination of a splitter device driver and their appliance attached to the SAN Fabric and TCP/IP network.

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Recovery Point/UNISYS 30MServer Server

RP Appliance

RP Appliance

WAN

FC Switch FC Switch

SAN SAN

All Data All Data

Duplicate ofWrite Data

Duplicate ofWrite Data

Data Lun

Journal Lun

Data Lun

Journal Lun

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Pros of Recovery Point/UNISYS 30M

• Low overhead on database server. Database server will see no more than 3% CPU overhead.

• Capable of many points to recover to.• Supports Bi-Directional Replication. Flow of

data is controlled through management interface.

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Pros of Recovery Point/UNISYS 30M

• Easy to use management interface.• Only replicates changed blocks since previous

replication.• Provides integrated FC/IP bridge. • Provides integrated WAN optimization.

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Cons of Recovery Point/UNISYS 30M• High price point.• Have to acquire additional disk on both SANs

to implement solution. This will accommodate the journals used for replication.

• Pay per TB being replicated. Every time you add storage that you want replicated you have to pay for this as well.

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Cons of Recovery Point/UNISYS 30M• Billed on the size of the LUN, not the actual

usage.• Need to buy additional appliances to get local

CDP and distance CDP. One replication appliance can replicate to one destination.

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SAN Based Replication Solutions

• SAN based replication solution. With this solution the SAN incurs the overhead of determining the changed blocks and sending them over to it’s mirrored pair.

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NetApp SnapMirror

Server

FC SwitchAll Data

All Data

Server

FC Switch

SAN

All Data

SAN

All DataWANRoute

rRouter

IP Switch IP Switch

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Pros of NetApp SnapMirror• Minor overhead on server when snapshot is

taken to start synchronization. This is done with their standard SnapDrive utility.

• Only sends the last change to a given block when a snapshot/replication event is triggered.

• Many alternatives for replication medium with FC or IP based replication paths.

• Can aggregate links to replicate more data in same amount of time.

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Cons of NetApp SnapMirror

• High price point.• Noticable jump in CPU Utilization for CPU

that has the SnapMirror daemon running on it.• The more data change between replication

intervals the more intense the CPU spike.• High level of planning to implement solution.

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EMC MirrorView /AServer

FC SwitchAll Data

All Data

Server

FC Switch

SAN

All Data

SAN

All DataWANRoute

rRouter

IP Switch IP Switch

FC-IP Bridge FC-IP Bridge

Primary Image Secondary Image

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Pro’s EMC MirrorView /A• No overhead to source server for

synchronization process. • Only sends the last changed blocks.• Flexible scheduling of when synchronizations

happen.• The amount of bandwidth the transfers

between SAN consumes is configurable.

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Cons EMC MirrorView /A

• Requires you to have a LUN in the Reserved LUN Pool for each mirrored pair (primary and secondary images).

• Each LUN in the Reserved LUN Pool must be large enough to handle any LUN participating in a SnapView or MirrorView relationship.

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Cons EMC MirrorView /A• You have to purchase a different product for

Synchronous replication.• If you configure the synchronization to run at

the highest rate it might affect throughput on the source LUN.

• Some models you have to purchase an external FC to IP bridge for WAN based replication solutions.

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SQL Server DR Things To Know• Take regular backups of all databases. Your

backup plan should include Full, Differential and Log backups. Frequent log backups help keep the size of the log file down.

• Verify you have good backups by restoring some of them on a regular interval.

• Move your backups to multiple locations. Having them stored on the main database server does you no good when that server crashes.

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SQL Server DR Things To Know• You can automate the exporting of all SQL

Server Agent Jobs, Operators, and Alerts you have defined. This can be done through the use of SMO.

• Know how to restore the system databases. – See this BOL article for the necessary steps to

restore the master database: http://msdn.microsoft.com/en-us/library/ms190679.aspx?s=1

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DR Plan Suggestions• Include thorough instructions to recover

system(s). Ideally this would be written so anyone would be able to understand it. Start simple, then add detail as you go. Something is better than nothing.

• Include names and phone numbers of co-workers as well as key customer contacts. A call plan works great in this scenario.

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DR Plan Suggestions

• Make it a living document. It should be reviewed at least twice a year. IT environments are constantly changing. That means you’re recovery plan does too.

• Test your plan, test your plan, and then test your plan some more.

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DR Plan Suggestions• Be sure to have your suppliers phone numbers

and key personnel in there too.• Stage simulated disasters to test your plan in a

realistic scenario.• Create an inventory of equipment you have so

you can easily replace it.• Move a copy of the most recent DR plan off

site to some place secure.

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Thanks, have a great night!

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Contact Information

Drew Flint

Plexus Systems Inc.

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afli@plex.com