Download - SQL Server 2014 AlwaysOn AG Failover
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Choirul AmriHead of Enterprise DivisionEbiz Cipta Solusi | [email protected]
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Session Objectives
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AlwaysOn Landscape – SQL Server 2014
Failover Cluster Instance(FCI)
• Instance level
• Shared storage
• Failover per instance
• No active secondary
• Support auto, transparentfailover
Availability Gro
• Database level
• No shared storage
• Failover per DB gr
• Active secondary
• Support auto, tranfailover
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Availability Groups Advantage
• No shared storage, easier and faster to implement
•
Active secondary for better box utilization‐ Offload reporting to secondary
‐ Backup from secondary
• Support automatic failover
• Transparent client failover
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What’s the “Groups” mean?
• Failover happens on “group of databases” rather than individual
• You can also create a group with only one database
•
Why: You want to make sure that related DBs are failed-over toget
Primary Server
CustomerDBTicketing
Secondary Server
CustomerDBTicketing
Jika Primary bermasalah:
Ticketing dan CustomerDB
dipindahkan bersamaan ke
secondary
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Availability Groups – Availability Mode
Asynchronous
• Better performance• Primary commits without waiting notification from
• Possible data loss in failover
Synchronous• Primary waits for notification from secondary bef
committing transaction
• Performance penalty
• No data loss during failover
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Availability Groups – Common Implementation
KOMODOSQL1 - Primary Server
CustomerDB
Primary Replica
Ticketing
Primary Replica
KOMODOSQL2 - Secondary Server
Readable Secondary
CustomerDB
Secondary Replica
Ticketing
Secondary Replica
KOMODOSQL3 - Secondary Server
Non-Readable (standby only)
CustomerDB
Secondary Replica
Ticketing
Secondary Replica
Synchronous
Asynchronous
Availability Listener
SQLAG-LS
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DemoPlanned – Manual Failover
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Failover Mode
Automatic
• Require Synchronous mode
• No data loss
• Machine shutdown or service unavailable
Planned - Manual
• Require Synchronous mode
• No data loss
• Use SSMS or T-SQL
Forced - Manual
• Replicas are in asynchronous commit mode
• Forced means: You can afford loosing data
• Obviously, data loss is possible
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Automatic Failover - Requirement
Requirement
• Minimum 1 pair databases are in Synchronous-commit with Autom
failover• Secondary databases are in synchronized state
• Windows Cluster is in good condition and fulfill the quorum require
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Automatic Failover – Ready to failover
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DemoAutomatic Failover
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Failover Mode – Real Life Scenario
Automatic
• Servers in the same data center with low latency network
• Unexpected machine crash or SQL service disruption
Planned - Manual
• Patching OS or SQL Server
• HA/DR exercise
• Upgrading hardware
Forced - Manual
• Real disaster happens – failover to DR site
• 3 servers, but 2 machines in primary DC are down
• There is no primary available in the configuration!
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Forced Manual Failover – Fixing “Resolving” con
What happen if:
1) KOMODOSQL2\SQL2014 is down; then
2) Client still can access the primary as usual (but now there is no “automatic” pa3) KOMODOSQL1\SQL2014 is down
4) Automatic failover to KOMODOSQL3\SQL2014 will not happen!
5) DBs in KOMODOSQL3\ SQL2014 replica is in “resolving” mode
6) Client application cannot connect
Server Instance Availability Mode Failover Mode Role
KOMODOSQL1\SQL2014 Synchronous commit Automatic Primary
KOMODOSQL2\SQL2014 Synchronous commit Automatic Secondary
KOMODOSQL3\SQL2014 Asynchronous commit Manual Secondary
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Recovering the “last man standing” node
Your situation:
• Primary and secondary in production are lost
• You only have 1 node in DR, but it is in resolving state, inaccessible f
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Bring Your “resolving” replica alive
--- YOU MUST EXECUTE THE FOLLOWING SCRIPT IN SQLCMD MODE
--- KOMODOSQL3 is the replica in resolving state
:Connect KOMODOSQL3\SQL2014
ALTER AVAILABILITY GROUP [KomodoSQLAG]FORCE_FAILOVER_ALLOW_DATA_LOSS;
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DemoRecovering from “Resolving” sta
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Q/A
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