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SQL Server Disaster Recovery
Detroit 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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Biography
Son – Ryan 4 Years Old
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Biography
Daughter – Emma 20 Months Old
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Agenda
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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
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–
–
–
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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. Replication
SQL Server Database
SQL Server Database
Table
Table
Publisher
Subscriber
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
Principal
Mirror
Partner DB Server
Partner DB Server
Witness DB Server
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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)
RXRC
Replication Client
VRR (RAM)
RXRC
Replication Client
Bitmap of
source volume
Bitmap of
source volume
Source Drive
Data
Data
Data
RXRS
Replication Server
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SAN
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 30M
Server
Server
RP Appliance
Duplicate of
Write Data
All Data
FC Switch
Journal Lun
Data Lun
SAN
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RP Appliance
WAN
Duplicate of
Write Data
FC Switch
All Data
Journal Lun
Data Lun
SAN
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
Server
Router
WAN
Router
All Data
All Data
SAN
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All Data
FC Switch
IP Switch
FC Switch
All Data
IP Switch
SAN
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 /A
Server
Server
Router
WAN
Router
All Data
All Data
All Data
FC Switch
FC Switch
FC-IP Bridge
SAN
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All Data
FC-IP Bridge
IP Switch
Primary Image
IP Switch
Secondary Image
SAN
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/enus/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 coworkers 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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[email protected]
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