1. High Availability in SQL Server 2012
Techniques to reduce downtime
Eric Peterson

2. Agenda Overview of SQL Sever Methods of High Availability
From hardware thru methods
not intended to teach how to implement
Tips given, tips accepted,
Review of methods, terms, features
Log Shipping
Replication
Mirroring
Clustering
Always On Availability groups
Other Things to think about.
Comparison on methods

3. Speaker Background 30+ years professional experience 70s Mainframe
80s Database
IDMS, IDSII, Oracle, Sybase
DB2 v1.6  DB2 2.0
90s Sybase Pro Serve
SQL Server, ODBC, PowerDesigner
Design and Beta Teams
00s Independent Consultant - MS SQL Server
Current - BCD Travel

4. High Availability, It Is All About the 9s
Downtime
Outage Seconds
Day
Week
Month
Year
½ min 30
1 min 60
5 min
300
10 min
600
15 min
900
30 min
1800
1 hour
3600
2 hours
7200
8 hours
28800
1 day
86400

5. High Availability (HA) Terms
Keeping the system up
Is Not Disaster Recovery
Recovering from when bad things happen
Latency
The amount of delay time it takes to synchronize between two systems
Temperature
Hot – Always up, always in Sync
Warm – Close, but has defined latency
Cold – manual intervention, defined loss

6. Methods Technologies that have an impact on HA Maintenance & Backups
Replication
Log Shipping
Mirroring Sync
Mirroring Async
Clustering
Always On Availability
Third Party Software

7. In the Beginning PCs in the post mainframe world Departmental apps
Single points of failure
Local disk drives
System board, Memory
Disk controller
Power supply
Backups ?maybe?
Loss of infrastructure
Network, etc

8. Resolving Single Points of Failure
Redundant
Power , Power Supplies
Battery/generator backup
Network cards
Device Controllers
Disks  SANs
Fault tolerant disks
RAID
Redundant Array of Independent Disks

9. RAID Levels Redundant Array of Independent Disks Raid 0 RAID 1
Block-level striping without parity
RAID 1
Mirroring without parity or striping.

10. RAID Levels
RAID 5
Block-level striping with distributed parity.

11. RAID Levels Raid 10 - Also known as Raid 1+0
A combination of RAID 1 and RAID 0
Mirroring + striping
No parity write – Faster for Inserts
Double the space!!!!
Hot Swap

12. RAID – Which is best BENCHMARK!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
If all things are equal –
“MPF” RAID 10
SAN Cache
If enough cache parity write may not impact performance
Device Controller dependent
Single Point of IO
If one disk corrupts then the other corrupts

13. More Redundancy is better
Hardware
SAN Replication, mirroring, copy, etc
Software Redundancy
Old School “BAR”
Replication
Log Shipping
Mirroring

14. Backup and Recover “BAR”
Manual or home grown process
Backup
Copy File
Restore Backup
Ability to query/develop against non production
Scrub production data
Latency defined
24 hours
1 week, month, quarter
Does not work as well for VLDB
Apply differentials

15. Replication Reads the Log Distribution Database Publisher Distributor
Keeps track
Publisher
Distributor
Can be on same SQL Server
Subscriber
One to many subscribers
Process can run in near real time
Can schedule as well

16. Replication Types Snapshot Transactional Replication Merge
Snapshot Agent
Schema and Data
Transactional Replication
One Way Publish to Subscribers
Incremental changes
Continuous or Scheduled
Merge
Merge Agent for Conflict Resolution
Every row is given a unique identifier
Detection and resolution

17. Replication Features Can Publish Stored Procs Monitoring Alerts
To non-SQL Server Subscribers
To Multiple Subscribers
Table by Table
Stored Procs
Monitoring
Alerts

18. Log Shipping Provides Backup of current DB in Secondary DB
Read Only Copy
Transaction Logs
“Shipped”
Automated “BAR”
SQL Agent Jobs
Latency
Schedule
Script Dis/Enable
One to Many DBs

19. Log Shipping Issues
Failover is not automatic you have to reset everything
Read only DB can be used in Manual Failover
Require application changes
When log is being applied,
Secondary read only DB connections are dropped
Network dependent
Log backup Size
Job Schedule default times
Spread schedule

20. Mirroring Dual Write for single DB on different SQL Servers
Asynchronous (High Performance)
Synchronous (High Safety Mode)
Good redundancy
Manual or Automatic failover
Rolling update
2008 Enterprise
Resolution of page errors

21. Mirroring Issues
Managing multiple databases so that if one fails they all fail is difficult if not impossible.
Synchronous needs to be close
Local or Dark Fiber
There is only one mirror of the database
The mirror is not directly usable it just sits there unless you are prepared to work with snapshots
There is no mirror after the failover, the mirroring state is DISCONNECTED and the principal is exposed
A SQL Server native client is needed to use mirroring

22. Clustering Overview SAN Node l Node N Cluster SQL Server Instance
Heartbeat
Node l
Node N
SQL Server Instance
Failover
SAN
Quorum Drive
Virtual Server Group
SQL Server
Windows
Server

23. Clustering Overview SAN Node l Node N Cluster SQL Server Instance
Heartbeat
Node l
Node N
SQL Server Instance
SAN
Quorum Drive
Virtual Server Group
SQL Server
Windows
Server
Failover

24. Clustering Terms Node Service Group(old) Resources Heartbeat Quorum
SAN

25. Cluster Setup Cluster is a logical grouping of Resources
Failover Cluster Manager (2008+)
Cluster Manager
Each Machine (node)
Windows Server
IP Address
Local and SAN Drives
Each (Service/Group) Instance
VM, windows server
SQL
Dedicated Resources

26. Cluster Failover Service/Group (VM) from one Node to Node
Best Available or Directed
Usually takes under 30 seconds
Automatic or Manual
Heartbeat Monitor
Application Independent
Failover Tracking
Failover Notification Proc
SQL Server Log
Cluster

27. Clustering Issues Failover usually fast Failover Issues
But can take several min to recover DBs
Failover Issues
Connections Drop
Transactions Stop
Failure to Connect
Cluster Can fail
SAN Disk Failure
Memory / Resources
Keep a spreadsheet

28. AlwaysOn Group/Cluster

29. AlwaysOn Terms Windows Server Failover Clustering Type
Always On Failover Cluster Instance
Always On Availability Group (cluster change!)
Can be either or both
Listener: IP Address and DNS Name
Logical Instance that programs attach
Replica:
SQL Server mirror copy of DBs

30. AlwaysOn Availability Groups
One Database or a Group of Databases
Advanced Mirroring
Multiple Secondary DBs
Multiple Synchronous DBs
Automatic Page repair
Active Secondary
Offloading workloads
Backup/log from secondary
Multiple Groups

31. AlwaysOn Availability
Database Group Failover
Automatic or Manual
Management Studio
Management of Groups in Management Studio
Dashboard
No Shared SAN
Local Attached disks
Ability to repair from mirror
Change raid level???

32. Mgmt Studio
Primary
Secondary
Listener

33. AlwaysOn Availability Restrictions
All servers must be in the same domain
Can be different data centers/cloud
Up to 3 replicas can be synchronous
Local, or dark fiber
Up to 2 of them can be used for automatic failover
All servers must use the same service account
If using Kerberos
Both AlwaysOn Availability (Group & Cluster )
Rely on Windows Server Failover Clustering infrastructure & Windows Cluster

34. AlwaysOn Failover Cluster Instance
Failover of the instance rather than at the DB level
New Features
Multi-site clustering across subnets for improved site protection.
Flexible failover policy for better control over instance failover.
Improved diagnostics for faster troubleshooting.
TempDB on local drive allows better query performance.

35. 2012 Always On Downside Failover time Two Machines two deploys for:,
Volume Dependent
30 seconds to 30 minutes
Two Machines two deploys for:,
Security
Must be same SID for SQL ids
SQL Agent
Jobs need to be “primary” aware
Secondary must be up bug
Corruption

36. SIOS Software Solution Overview
Cluster
Heartbeat
Node l
Node N
SQL Server Instance
Failover
VM SAN
Quorum Drive
Virtual Server Group
SQL Server
Windows
Server

37. Comparison of Methods * Maintenance - use most current versions Type
Latency
Temp 9s HA DR
Replication
asynchronous - scheduled
warm
Manual
Application must handle
Very Good
Backup
daily
cold OK
Log Shipping
Scheduled
Cold - warm
good to excellent.
Mirroring (Sync)
synchronous
hot
good
monitor server
very good
Mirroring (Async)
depends on volume
manual
Clustering
N/A
excellent
excellent to poor for SAN failure
Always On (Sync)
Always On (Async)
warm +
* Maintenance - use most current versions

38. Maintenance Beyond Patch Tuesday Backups Index/Table fragmentation
Clustering
Backups
Tape Drive speed
Index/Table fragmentation
Online index
Old Data Removal
Size matters, smaller is better

39. What's Best for your environment?
If you are afraid to failover
You do not have a valid system
Define the 9s thru Legal Cheating
Change the calculation
Yes/No
Remove scheduled maintenance time from calc time
Change the definition
SQL > Cluster
Benchmark
Knowledge