SQL AlwaysOn Availability Groups Tomislav Balaž

Sadržaj Što je AlwaysOn Availability groups Feature? Koristi koje nam donosi AlwaysOn FCI vs AO Database Mirroring vs AO Preduvjeti Napomene Novo u SQL 2016 Demo

Što je AlwaysOn Availability Groups Feature? AlwaysOn Availability Groups feature is a high-availability and disaster-recovery solution that provides an enterprise-level alternative to database mirroring. Dostupan je od verzije 2012 Potrebna verzija je Enterprise

Kakve koristi nam donose AG Jedna primarna Availability replica i do osam secondary Availability replica Synchronous i Asynchronous commit mode Tri tipa failover-a Active secondary replica (Read-only ili Backup) Availability Listener za svaku AG Failover Policy AlwaysOn Dashboard i PowerShell cmdlets Replica je instanca baze na drugoj instanci SQL servera Asynchronous-commit mode. This availability mode is a disaster-recovery solution that works well when the availability replicas are distributed over considerable distances. Synchronous-commit mode. This availability mode emphasizes high availability and data protection over performance, at the cost of increased transaction latency. A given availability group can support up to three synchronous-commit availability replicas, including the current primary replica. automatic failover, planned manual failover (generally referred as simply "manual failover"), and forced manual failover (generally referred as simply "forced failover") U SQL serveru 2016 moći ćemo definirati failover ako je baza corruptana kroz AG health monitor (verzija 2014 gleda samo health SQL instance) http://download.microsoft.com/download/D/7/5/D750D5B9-8692-42FC-80D8-0EA9C3E76739/SQL_Server_2016_Mission_Critical_Performance_White_Paper.pdf (str. 20)

Usporedba FCI vs AllwaysOn Nodes within an FCI Replicas within an availability group Uses WSFC cluster Yes Protection level Instance Database Storage type Shared Non-shared Storage solutions Direct attached, SAN, mount points, SMB Depends on node type Readable secondaries No Applicable failover policy settings WSFC quorum FCI-specific Availability group settings Failed-over resources Server, instance, and database Database only

Usporedba Databse Mirroring vs AllwaysOn Database Mirroring AlwaysOn Availability Groups Maximum number of secondary databases 1 Mirror 4 Secondaries Requires Windows Clustering No Yes, however the SQL Servers can be stand-alone Automatic failover Yes, requires witness server and high-safety mode Yes, one HA or DR Choose one Each secondary independently configurable Groups of databases No, each database is configured separately Multiple databases can be grouped to failover together Offload backups Yes Connection to active database Requires special connection string for failover Redirection handled by Windows Clustering with a virtual name. Special connection string not required Connection string to mirror or secondary database N/A ApplicationIntent connection string to automatically redirect or can use traditional connection string with server name.

Preduvjeti Windows Server 2008 ili noviji SQL Server 2012 .Net framework 3.5.1 Node u WSFC Hotfixes ako koristite Windows Server 2008 ili 2008R2 Ne na DC Svi SQL serveri moraju imati isti collation Enable AllwaysOn Availability groups Link: https://msdn.microsoft.com/en-us/library/ff878487(v=sql.110).aspx#SystemRequirements Checklist https://msdn.microsoft.com/en-us/library/ff878487(v=sql.110).aspx#SystemRequirements

Napomene Enterprise edition Brisanje baze, gubitak data file-ova ili corruption transaction loga ne uzrokuju failover Server configuration settings, Credentials, Jobs, Cros-Database queries, Linked servers… System databases ne mogu biti dio AG Baze moraju biti u Full recovery model DB replike moraju biti na različitim nodovima u FC Link: https://msdn.microsoft.com/en-us/library/ff878487(v=sql.110).aspx

Novo u SQL 2016 3 synchronous replicas for auto failover Loadbalancing on read only replica Automatic failover on database health Link: http://download.microsoft.com/download/D/7/5/D750D5B9-8692-42FC-80D8-0EA9C3E76739/SQL_Server_2016_Mission_Critical_Performance_White_Paper.pdf

Setup 1. Create Cluster 2. Add nodes to cluster 3. Setup file share majority 4. Enable AllwaysOn 5. Create Availability Group 6. Backup database 7. Add database to Availability group 8. Failover

Demo 1. Availability group wizard 2. Read only replica 3. Backup replica 4. Test failover Pokazati wizard i objesniti svaki dio wizarda. Kreirati read only replicu Pokazati backup on secondary Pokazati failoverpolicy Test failover

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