Disaster Recovery and High Availability, Overview of

8/6/2019 Disaster Recovery and High Availability, Overview of

http://slidepdf.com/reader/full/disaster-recovery-and-high-availability-overview-of 1/19

CoCreative Solutions

How Microsoft SQL Server caters to

Disaster Recovery (DR)High Availability (HA)

Paul PaivaCoCreative Solutions, LLC

[email protected]

http://paulpaivasql.blogspot.com

April 19, 2011

Overview of DR and HA




DR vs. HA

• Disaster Recovery

– If there is a natural or human-induceddisaster, can we recover?

• High Availability

– How much downtime is acceptable?

– What is the customer’s SLA?




3 Recovery ModelsBackups can beconfigured with threedifferent recovery

models

•Simple•Full

•Bulk-logged

See:

Database Properties,

Options tab




DR – 3 Backup Models

1. Simple

– Advantages• No need for log backups.

• Easier to manage, less files.

– Disadvantages• Can recover only to the last backup.

– Appropriate if

• There is a way to manually re-enter data to point offailure.

• Data changes infrequently.




DR – Backup Models

2. Full

– Can recover to the last transaction log

• Point-in-time restore is possible.

– to last Time, Mark, or Log Sequence Number (LSN)

– Backup Transaction Logs periodically• Hourly, every 15 minutes, etc.





Differential

• Only backups portions of database/file that havechanged since the last full backup.

• Advantages – File sizes are smaller

– No need to apply all the transaction logs.




Point-in-Time Restore

From SQL Server BOL





3. Bulk Logged

– Can recover to the last transaction log

• Point-in-time is not supported




Backup Syntax




Script a Simple Backup for All Databases




Other Backup Options

– Copy_Only• Does not interrupt the sequence of transaction log backups

– Compression

• SQL 2008, enterprise edition• SQL 2008 R2, all editions

– File or Filegroup only

• Useful when only one or more tables need to be

safeguarded. – Snapshots




High Availability

• How much downtime is acceptable?




HA - Methods

• Replication

– Peer-to-Peer (transactional) – Publisher/Subscriber model

– Allows only certain objects to be replicated

– Object schema must be identical – Schema changes require system to be quiesced.

– Some overhead: distributor needs to be configured

and maintained. – Data conflicts can be introduced and need to be

resolved.




HA - Methods

• Failover Clustering

– for whole SQL Instance (all databases aresafeguarded)

– Nodes need to be in close proximity to each other

– Auto failover

– Does not protect against disk failure• Nodes share the same disk.

• Disk files on RAID

– Arguably the best method for most stringentrequirements

• Most expensive, most work involved to configure, morehardware required.




HA - Methods

• Database Mirroring

– One database is safeguarded (at-a-time) – Consists of a Principal and Mirror database

– Synchronous

• Safest – the mirror is always in synch.• Auto-failover is possible by using a 3rd machine, a

Witness

– Asynchronous• allows faster speeds, however some latency maydevelop




HA - Methods

• Log Shipping

– One database (at-a-time) is safeguarded

– Very simple, easiest to maintain

– Primary and backups can be separated by fardistances.




Fallback Server

• A human-introduced error will immediately

propagate to the other cluster nodes ormirror nodes.

• Remedy: Lagging Fallback Server

– Configure a fallback server to receivetransactional logs

– Make it lag the production database




Summary

• DR

– As a rule, use FULL backup model – Store copy of back ups off site

• HA

– Clustering (high cost)• auto failover

– Mirroring (per database)• auto failover

– Log Shipping (per database)• Can be configured to have a lag

– Replication (per object)



CoCreative Solutions Introduction to

DR and HA

• Thanks for your time and attention!

• Questions?

Paul Paiva

CoCreative Solutions, LLC

[email protected]://paulpaivasql.blogspot.com

April 19, 2011

Documents

Disaster Recovery and High Availability, Overview of