1. Always On : Multi-site patterns
John Q. Martin
Always On : Multi-site patterns

2. BIG Thanks to SQLSat Denmark sponsors

3. About Me John Q. Martin Product Manager for SentryOne
Microsoft Data Platform MVP
Over a decade of experience with SQL Server as a Dev, DBA and BI Dev. Most recently working as a Premier Field Engineer with Microsoft UK.
Contact Info
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4. What is Always On?

5. Definitions – HA & DR
Highly Available systems are comprised of systems configured to maintain service availability in the event of hardware failure on the primary site, highly available systems should result in less than five minutes of downtime when an event occurs and should involve no manual intervention. Data systems should be fully consistent and have no data loss other than that which was in-flight at the time of the event that caused the failover.
Disaster Recovery systems are comprised of elements that can be brought online in the event of an issue to the main business site that results in the inability to perform business operations. It is anticipated that in the event of a Disaster situation the DR process will be enacted after a decision by the senior management of the business. In the event that the Disaster process is activated, the Disaster Recovery process should bring the platform online and ready for business transactions in no more than six hours with no more than fifteen minutes of data loss to the business.

6. Why Multi-Site?

7. Multi-site considerations

8. Failover Cluster Instances [FCI]
Multi-Site : High Availability
Region : UK South
FSW
Site 1
Site n.
WSFC
Storage Synchronisation

9. Availability Groups [AG]
Multi-Site : High Availability
Region : UK South
FSW
Region : West Europe
Region : North Europe
Windows Server Failover Cluster
[Asynchronous]
[Synchronous]
[Synchronous]
Replica : Primary
Replica : Secondary
Replica : Secondary
Replica : Secondary

10. Availability Groups [AG]
Multi-Site : High Availability
Region : UK South
FSW
Cloud Witness
Region : West Europe
Region : North Europe
Windows Server Failover Cluster
[Asynchronous]
[Synchronous]
[Synchronous]
Replica : Primary
Replica : Secondary
Replica : Secondary
Replica : Secondary

11. Availability Groups [AG]
Multi-Site : High Availability
Region : UK South
FSW
Region : West Europe
Region : North Europe
Windows Server Failover Cluster
[Asynchronous]
[Synchronous]
[Synchronous]
Replica : Primary
Replica : Secondary
Replica : Secondary
Replica : Secondary

12. Availability Groups [AG]
Multi-Site : High Availability
Region : UK South
FSW
Cloud Witness
Region : West Europe
Region : North Europe
Windows Server Failover Cluster
[Asynchronous]
[Synchronous]
[Synchronous]
Replica : Primary
Replica : Secondary
Replica : Secondary
Replica : Secondary

13. Availability Groups [AG]
Multi-Site : Disaster Recovery
Region : West Europe
Region : North Europe
FSW
Windows Server Failover Cluster
[Asynchronous]
Replica : Primary
Replica : Secondary
Replica : Secondary
Replica : Secondary
Replica : Secondary

14. Multi-Site : Stretch Clusters
Cluster Settings
CrossSubnetDelay
CrossSubnetThreshold
Allow for greater latency and unreliable link between sites.*
Controls the IP Addresses that will be registered in DNS & the Time To Live (TTL).
Cluster Settings
RegisterAllProvidersIP
HostRecordTTL
Where there is a stretch VLAN in place that results in all of the cluster nodes being in the same IP Subnet then the SameSubnetDelay and SameSubnet Threshold cluster parameters will need to be set appropriately.
Affects whether a node can participate in forming quorum.
Cluster Settings
NodeWeight

15. Cluster Heartbeat Settings
CrossSubnetDelay CrossSubnetThreshold
|CrossSubnetDelay
| Default : 1000
| Max : 4000
|CrossSubnetThreshold
| Default : 20
| Max : 120
Time to initiate Failover
| CrossSubnetDelay x CrossSubnetThreshold
Subnet : /24
Subnet : /24

16. Cluster Heartbeat Settings
SameSubnetDelay SameSubnetThreshold
|SameSubnetDelay
| Default : 1000
| Max : 2000
|SameSubnetThreshold
| Default : 10
| Max : 120
Time to initiate Failover
| SameSubnetDelay x SameSubnetThreshold
Subnet : /24
Subnet : /24

17. Cluster Heartbeat Settings

18. Availability Groups [AG]
Multi-Site : Disaster Recovery
Distributed Availability Group [Distributed AG]
Region : West Europe
Region : North Europe
FSW
FSW
Windows Server Failover Cluster
Windows Server Failover Cluster
[Asynchronous]
Replica : Primary
Replica : Primary
Replica : Secondary
Replica : Secondary
Replica : Secondary
Replica : Secondary

19. Azure Availability Configurations
Devil in the detail
Availability SLA requirements
Single or multiple machines, depending on storage
Allocates VMs to Fault Domains and Upgrade Domains
Who’s fault is it?
Use Availability Sets
GROUP BY
Resource Groups
Regions
Resource Groups are global for logical grouping of services

20. Summary Identify multi-site requirement Be aware of latency impact
High Availability Or Disaster Recovery
Recovery Point/Time Objectives
Be aware of latency impact
Log synchronization
Storage synchronization
Failover Cluster Services configuration
Service Dependencies

21. Questions?
???

22. BIG Thanks to SQLSat Denmark sponsors