sql server high availability tim beamer, technology evangelist, dell services...
TRANSCRIPT
Global Marketing
Patching & Service Pack InstallationHardware and Software UpgradeSystem ReconfigurationDatabase MaintenanceApplication Upgrade
Human Error #1 Cause of FailureSite DisastersHardware MalfunctionData CorruptionSoftware Crash
Availability during Planned Downtime
Protection against Unplanned Downtime
Downtime causes lost customer revenue and decreased staff productivity
Why Do You Need High Availability?
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Conceptual Design, SQL 2005
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Conceptual Design, SQL 2008
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SQL Server 2008 High Availability
Redundancy at server, database and data page levels reduces costs associated with
downtime
Highly credible, cost effective high availability solutions
Reduced downtime for database maintenance and hardware upgrades
Reduced contention for resources
Increased availability of data in the event of a partial failure
Industry leading manageability tools
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Agenda
• Increasing Availability
• Decreasing Downtime
• Improving Manageability
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SQL Server 2008 High Availability Features
Database Mirroring
Transactional Replication
Log Shipping
Backup/Restore
Windows Clustering
Database Snapshot
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Database MirroringOverview
• Hot Standby protects against database or server failure
• Provides a fault-tolerant database
• Cost effective as no specialist hardware is required
• Straightforward setup and administration
• Automatic or manual failover– SQL Server 2008 does not require a database restart after
manual failover
• Automatic, transparent client redirect
• No shared components; two separate copies of data
• SQL Server 2008 compresses the log stream from Principal to Mirror
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Principal Mirror
Client
Witness
Database MirroringSynchronous, high availability configuration
Data is mirrored synchronously as part of a transaction
Automatic failover if Principal server fails
Automatic Client redirection
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Principal Mirror
Client
Database MirroringSynchronous, high protection configuration
Data is mirrored synchronously as part of a transaction
Manual failover if Principal server fails
Automatic Client redirection
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Principal Mirror
Client
Database MirroringAsynchronous, high performance configuration
Data is mirrored asynchronously outside of transactions
Manual failover if Principal server fails
Automatic Client redirection
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Database MirroringRecovering suspect pages
• SQL Server 2008 uses a checksum to validate page writes
• Inconsistant pages can be recovered automatically from the mirror server
Principal Mirror
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Transactional Replication• High performance – latency measured in seconds
• Minimal load on the server
• Cost effective as no specialist hardware is required
• Straightforward setup and administration
• Can be implemented at database or table level
• Two types– Standard transactional replication
› Easy to design, setup & manage› Subscriber (standby) can be used for reporting
– Peer-to-peer transactional replication› Multi-master model; schema is identical on all sites› Supports distributed applications with data partitioning;
enables load balancing› Does not handle conflicts; design to avoid/prevent conflicts
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Transactional ReplicationReplication Options
New Jersey
Transactional ReplicationReporting + Redundancy
Peer-to-Peer ReplicationQuery Scale Out + Redundancy
New York
Boston
Seattle Tokyo
Shanghai
London
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Distribution Agent
DistDB
Logreader Agent
Distribution Agent
DistDB
Logreader Agent
Distribution Agent
DistDB
Logreader Agent
“West” “East”
“South”
Peer-To-Peer Transactional ReplicationHow does it work?
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Peer-To-Peer Transactional ReplicationSQL Server 2008 Enhancements
• Configure replication easily with the new graphical topology viewer
• Add new nodes without taking replication offline
• Protect against accidental conflicts with SQL Server 2008 conflict detection
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Log Shipping
• Provides database redundancy
• Cost effective as no specialist hardware is required
• Straightforward setup and administration
• Running read operations such as reports on secondary server is permitted– Users are disconnected when log
restore occurs
• Can maintain multiple secondary servers
• Optional Monitor server– Records history and status of
backup/restore jobs
– May be setup to raise alerts when jobs fail
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Backup
• Permanent copy of data
• Online restore– Perform a restore operation while an
instance of SQL Server is running
• Backup compression in SQL Server 2008– Reduce volume by up to 50%– Allows reduced latency and faster
restore– Applied per instance and per backup
• Cost effective - no specialist hardware is required
• Straightforward setup and administration
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BackupBackup Media Mirroring
• Protection against lost or damaged backup media– All backup types can be mirrored (database, log, etc.)
– Each device must be the same type
– All devices must be present during Backup, but only one backup set is required for Restore
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Microsoft Clustering
• Server hardware redundancy – Using a shared disk subsystem
– Entire instance virtualized and fails over as a unit
– Can include non-SQL Server resources
– SQL Server 2008 no longer requires a drive letter for each instance
• Clustering can be combined with Database Mirroring, Log Shipping, or Replication
• Geographically Dispersed Failover Clustering provides protection even if the disk array fails
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Microsoft ClusteringSQL Server Editions
Standard Edition
Enterprise Edition
2-node clusters only As many nodes as the operating system supports
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Windows Server 2008 Clustering
Support for 16 node clusters
Nodes can reside on different subnets
Support for OR dependencies•E.g. Network Name resource is available if either of two IP Address resources is available
Cluster Validation tool•Verifies adequate hardware resources for clustering
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Database Snapshot
• Provides a read-only, consistent copy of database
• Snapshot remains unchanged while database is modified
– Protects against user error and data corruption
• Very fast to create
• Preserves disk space– “Copy-on-Write” technology
• Can be created for any database
• Cost effective as no special hardware is required
• Straightforward setup and administration
Client
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Putting it All Together
Database Mirroring
Logical RecoveryStandby
Log Shipping
Log Shipping with Restore Delay
ProductionDatabase
Replication
Clustering
Database Mirroring Primary disaster site for databases
Log Shipping Additional disaster sites for
databases Logical Recovery
Replication Database reporting and read
scale out with redundancy
Clustering Local server redundancy
Always On Storage Partner Solutions Site storage HA Highest hardware reliability
WarmStandby
HotStandby
DatabaseScale OutFor Queries
Backup
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SQL Server High Availability Licensing
License only active servers
• Passive servers do not require a license• If a failover occurs a license is not required for 30 days
Most cost effective high availability model amongst leading database vendors
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Agenda
• Increasing Availability
• Decreasing Downtime
• Improving Manageability
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Enhanced Restore Operations
Online Restore
• Access restored data even when the rest of the database is not yet available
Piecemeal Restore
• Recover the database in stages – bring critical filegroups online first, then restore remaining filegroups
Page-Level Restore
• Restore individual pages from a backup to resolve page corruption issues quickly
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Fast RecoveryDuring Restart or Restore
• SQL Server 2000– Database is available after Undo completes
• SQL Server 2008– Database is available when Undo begins
UndoRedo
DB is Available
Time
UndoRedo
DB is Available
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Online Index Operations
• Create, Rebuild, and Drop indexes online
CREATE CLUSTERED INDEX idx_PrdON ProductsWITH (ONLINE = ON)
Source(Existing Products table)
Target(new index)
SELECT
INSERTUPDATEDELETE
ScanSort/MergeBulk Insert
Idx_Prd
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Partial Database Availability
• Database remains partially available when secondary files are damaged
Primary Filegroup
Additional Data Filegroups
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Locking and Concurrency
Row versioning support
• READ_COMMITTED_SNAPSHOT isolation level• ALLOW_SNAPSHOT_ISOLATION database option
Benefits of row versioning
• Read operations retrieve a consistent snapshot of the database.• SELECT statements do not lock data during a read operation (readers do not block writers, and vice versa)• SELECT statements can access the last committed value of the row, while other transactions are updating the row without getting blocked• The number of deadlocks is reduced• The number of locks required by a transaction is reduced, which reduces the system overhead required to manage locks• Fewer lock escalations take place
Enhanced locking in SQL Server 2008
• Optimized lock escalation for partitioned tables and indexes
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Dynamic Configuration
Hot-Add Memory
Hot-Add CPU
Add hardware resources without taking the database server offline
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Agenda
• Increasing Availability
• Decreasing Downtime
• Improving Manageability
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Table and Index Partitioning
• Partition tables and indexes across multiple physical files– Reduce the impact of IO intensive
operations
– Manage backup and archival based on partitions
– Control lock escalation at the partition level to increase concurrency
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Dedicated Administrator Connection
Special diagnostic connection for administrators
• Available when other connections are not possible• Use to troubleshoot or shut down cleanly• Only available from clients running on the server
by default
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Resource Governor
• Ability to differentiate workloads– e.g. app_name,
login, etc.
• Per-request limits– Max memory %– Max CPU time– Grant timeout– Max Requests
• Resource monitoring
SQL Server
Admin Workload
Backup
Admin
TasksReport WorkloadOLTP Workload
OLTP Activit
y
Executive
ReportsAd-hoc Reports
High
Min Memory 10%Max Memory 20%
Max CPU 20%
Admin Pool
Max CPU 90%
Application Pool
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Tim’s Axioms of DR
• A failure to plan is the plan for failure
• If you’re building the plan while recovering, make sure your resume is updated
• The failure to plan on someone else’s part will almost always constitute an emergency on your part
• Plan for the worst, hope for the best, and know that reality is always somewhere in the middle
• Commitment = $
• Every plan has a weak link, identify early and strengthen
• Regular review is critical
• Always have a “Plan B” ready to go
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Planning Considerations
• Plan development will require input from every business unit
• RPO/RTO needs to be well-defined and well-aligned
– If the RTO for SQL is 2 hours and an application using SQL has an RTO of 10 minutes, your alignment is off
– “A week” is NOT a well-defined RTO
• RPO/RTO define the solution, NOT the other way around
• Develop your Application Matrix (communicate it too)
• Document dependencies (Dynamics CRM requires SQL, Exchange, Scribe, and LOB App X)
• Each additional place to the right of the decimal for uptime is an exponential increase in the cost of the solution (99.9% vs. 99.99%)
• Designate alternates for each role/responsibility
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Can Virtualization help?
• Of course!
• HW virtualization (Live Migration, V-Motion)
• Storage Virtualization (Quick Storage Migration ,Storage V-Motion)
• Storage Solutions with SQL “intelligence” (Like Equallogic and Compellant) to reduce admin involvement
• COMBINE your D/R and Prod. Environments
• Don’t forget about the End-User environment– Desktop
– Applications
• Have you thought about “cloud”?
Q&A