Navigating the options for Data Redundancy Wendy Pastrick SQL Server MVP BI Consultant, BlueGranite, Chicago

About Wendy DBA since 2000 Professional Association for SQL Server member and volunteer Chicago Suburban SSUG Chapter

AGENDA Defining High Availability A Brief Overview Replication Log Shipping Mirroring Clustering How to Choose Which to Use? Pros and Cons Compare and Contrast

High Availability Different than Disaster Recovery Is full failover necessary? How much downtime is acceptable? Are personnel available to assist in a failover? What hardware resources can be utilized? What is the physical distance between servers? More options than what is covered in this presentation!

Replication Transactional, Peer-to-Peer and Merge options Publishers and Subscribers Distribution database All databases available for use Most flexibility with replication option Can be complex and monitoring required

Transactional Replication Push or Pull subscribers

Peer-to-Peer

Merge Replication Push or Pull Subscribers Conflict Resolvers as All subscribers can be updated

Replication Use Case Distributed Subscribers Reporting Needs

Log Shipping Transfer and application of Log File Backups Primary to Secondary SQL Agent Jobs Fileshares required Option to have Secondary database in Standby mode for ReadOnly access

Log Shipping Topology

Log Shipping Use Case Read Only Scenario Built in Delay possible security benefit possible data retrieval

Mirroring Transactional Application from Logs Principal to Mirror Utilizes End Points Synchronous Asynchronous Endpoint: An endpoint is a SQL Server object that enables SQL Server to communicate over the network. It encapsulates a transport protocol and a port number.

Mirroring Topology Synchronous vs Asynchronous Synchronous – wait for commit on Mirror Asynchronous – faster, but some risk of data loss Synchronous vs Asynchronous

Mirroring Use Case Geographically dispersed cluster Poor man’s cluster

Clustering AlwaysOn Availability Groups Database Level Windows Server Failover Cluster Instance Level

Availability Groups

Failover Clustering

Pros Replication Log Shipping Mirroring Multiple database support All copies are fully functional databases Log Shipping Simple setup Witness for monitoring Can use Secondary as Read-Only Mirroring Automatic, Immediate Failover Least potential for data loss (in Synchronous mode) Can use a snapshot for Read-Only of Mirror instance

Cons Replication Log Shipping Mirroring Complex setup Publications can expire Transactions can experience backlog/blocking Manual Failover Log Shipping Asynchronous Only Mirroring Single Database Only Physical Distance issues

Contrast Availability of data Time and effort to failover Fully Recovered vs. Read-Only Time and effort to failover Automatic vs. Manual Number of databases supported One vs. Many

Summary Any of these are viable High Availability solutions Make a list of questions and ensure Management is in agreement with the answers Consider the available hardware and additional resources required

Resources http://www.sqlbackuprestore.com/introduction.htm http://sqldbpool.com/2010/02/15/database-mirroring-vs-log-shipping/ http://technet.microsoft.com/en-us/sqlserver/gg508900.aspx

Where to Find Me Wendy.Pastrick@sqlpass.org @wendy_dance on Twitter Blog: wendyverse.blogspot.com http://www.linkedin.com/in/wendypastrick