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

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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 Twitter : @SQLDiplomat Email : Jmartin@SentryOne.com Blog : http://blogs.SentryOne.com/author/JohnMartin/ LinkedIn : https://uk.linkedin.com/in/johnqmartin

What is Always On?

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.

Why Multi-Site?

Multi-site considerations

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

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

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

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

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

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

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

Cluster Heartbeat Settings CrossSubnetDelay CrossSubnetThreshold |CrossSubnetDelay | Default : 1000 | Max : 4000 |CrossSubnetThreshold | Default : 20 | Max : 120 Time to initiate Failover | CrossSubnetDelay x CrossSubnetThreshold Subnet : 192.168.0.0/24 Subnet : 192.168.1.0/24

Cluster Heartbeat Settings SameSubnetDelay SameSubnetThreshold |SameSubnetDelay | Default : 1000 | Max : 2000 |SameSubnetThreshold | Default : 10 | Max : 120 Time to initiate Failover | SameSubnetDelay x SameSubnetThreshold Subnet : 192.168.0.0/24 Subnet : 192.168.1.0/24

Cluster Heartbeat Settings

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

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

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

Questions? ???

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