Microsoft SQL Server Disaster Recovery and Availability

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Microsoft SQL Server Disaster Recovery and
Availability
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Definitions(http//www.microsoft.com/windowsserve
rsystem/storage/storgloss.mspx)

• From glossary http//www.microsoft.com/windowsserv
  ersystem/storage/storgloss.mspx
• Business ContinuityThe ability of an
  organization to continue to function even after a
  disastrous event, accomplished through the
  deployment of redundant hardware and software,
  the use of fault tolerant systems, as well as a
  solid backup and recovery strategy.
• Disaster RecoveryThe ability to recover from
  the loss of a complete site, whether due to
  natural disaster or malicious intent. Disaster
  recovery strategies include replication and
  backup/restore.
• Note that DR-related terms are used very
  inconsistently. Be certain that all parties in
  your organization understand and use agreed-upon
  definitions in order to avoid confusion.

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Definitions (cont.)

• For clarity, well use the following definitions
  today
• Disaster an event that results in serious loss
  of data or service
• Disaster Recovery A process that allows
  continuation of business following a disaster,
  including manual methods
• Offsite Disaster Recovery A process that allows
  disaster recovery at a remote location (usually
  entire site)
• Business Continuity A process that includes
  disaster recovery and offsite disaster recovery
  as well as using systems to avert disasters, such
  as fault-tolerant hardware and software

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Definitions (cont.)

• From http//support.microsoft.com/kb/822400/en-us
• Disaster recovery planning is the work that is
  devoted to preparing all the actions that must
  occur in response to a disaster. The planning
  includes the selection of a strategy to help
  recover valuable data. The selection of the
  appropriate disaster recovery strategy depends on
  your business requirements.

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Definitions (cont.) Disaster and Recovery
Examples

• Data are deleted from a critical application
  table
• Perform point-in-time recovery to time of problem
• A network hardware failure prevents a database
  server from being accessed over network
• Wait for hardware to be replaced
• Fail over to warm standby
• Fail over to hot standby
• 2 drives fail in a RAID-5 disk array
• Replace hardware and restore from backups
• Fail over to warm standby
• Fail over to hot standby
• Fire disrupts all electric power to data center
• Wait for service to be restored
• Implement offsite disaster recovery plan
• An earthquake levels company headquarters
• Implement offsite disaster recovery plan

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Business Continuity Planning

• Business continuity requirements are driven by
  internal/external customer service level
  agreements (SLAs)
• How much data loss is permissible
• How long can application be unavailable
• What is the minimum service level required (e.g.
  online response time following a fail-over) and
  maximum permissible time in degraded state
• Different applications will have different SLAs
• Management must
• Consider additional cost of redundant facilities,
  equipment, software, administration, testing,
  etc.
• Evaluate risks of added complexity
• Balance real (hard-dollar) costs of Business
  Continuity scenarios against the likelihood of
  such a scenario actually occurring

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Business Continuity Planning (cont.)

• Discuss different scenarios with business users
  to manage expectations
• Include specific scenarios in BC documentation
• Recovery must be tested regularly
• DR plan also includes switching back to primary
  hardware/site

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Business Continuity (cont.)System Availability
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Business ContinuitySummary

• Business Continuity is a spectrum of strategies
  and solutions from 24x7x365 availability through
  no recovery at all
• Even the best BC plan cannot anticipate all
  recovery scenarios some ad-hoc procedures may
  be needed during implementation to minimize data
  loss