1. SQL Azure Database – High Availability
Jan 2018 – SQL Saturday Malaysia 2018
Nagaraj Venkatesan,
Data Platform MVP, Singapore

2. SQL Azure DB – HA / DR High Availability Backup n Restore
Active Geo Replication
Active Geo Replication + Failover Groups
Active Geo Repl + FG + Elastic Pools

3. Default Backup Options
Automatic Full, differential and T Log
Local and Geo redundant
Automatic backup
7 days for basic, 35 for standard, premium
Long Term Retention for extended retention
Retention
Local Redundant – Any time
Geo Redundant – 1 hour, 12 hours recovery time
RPO / RTO
Not suitable for mission critical workload
Can’t do load sharing
Challenges

4. Geo Replication Fundamentals
Primary
Secondary
Asynchronous
Active Secondary
Upto 4 secondary
Read Only Queries
Service Tier
Available on all service tier
Primary n Secondary – Same tier
Pricing n DTU
Secondary can have lesser DTU than primary
Secondary Pricing – Same like Primary

5. Geo Replication Fundamentals
Primary
Secondary
Asynchronous
Avoiding Data Loss
Exec sp_wait_for_database_copy_sync
Sizing Secondary
Log IO % * Primary DTU
Sys.dm_db_resource_stats

6. Comparison – RTO, RPO Capability Basic tier Standard tier Premium tier
Point in Time Restore from backup
Any restore point within 7 days
Any restore point within 35 days
Geo-restore from geo-replicated backups
ERT < 12h, RPO < 1h
Restore from Azure Backup Vault
ERT < 12h, RPO < 1 wk
Active geo-replication
ERT < 30s, RPO < 5s

7. Transparent & Auto Failover
Failover Groups

8. Failover Groups – ( Preview )
What is it
Transparent failover like always on
Read Write and Read Only URL
Secondary
Max 2 secondary
Same subscription
Failover
Automatic or Manual
Multiple DBs
GracePeriod - Wait time before failover with data loss

9. Failover Group Application FAILOVER GROUP LISTENER Intent = Read Only
Intent = Read /Write
Intent = Read Only
Intent = Read /Write
Primary
Secondary
Secondary
Primary
Asynchronous Synchronization
Failure

10. Failover Groups - Monitoring
sys.dm_geo_replication_link_status
replication_state_desc – Expect to see “catch-up”
replication_lag_sec – Time to sync up lag
last_commit – Time upto which secondary has caught up
sys.dm_operation_status;
Geo Replication Setup details

11. Multiple databases – cost effective solution
Elastic pools

12. Elastic Pools Elastic Pool 150 DTU DB1 100 DTU DB1 AVG usage – 40 DTU
Peak – 80 DTU
DB2
100 DTU
DB2
DB3
100 DTU
DB3

13. Assume 3 DBs peak simultaneously
Elastic Pools
Normal SQL Database
10 Databases
100 DTU each
AVG: 40 DTU
MAX: 80 DTU
Total DTU = 100 * 10 = 1000 DTU
COST: 1.5 * 1000= 1500 USD
Elastic Pool
Assume 3 DBs peak simultaneously
10 Databases
AVG: 40 DTU
MAX: 80 DTU
Total DTU: (( 80 * 3 ) + ( 40 * 7 ) )
= = 520 DTU
= 2.25 * 520 = 1170 USD

14. Elastic Pools Multiple DB with Varying Workload
Avoids over / under provisioning
Elastic Pools
Predictable price
1.5 times Single DB DTU cost
Suitable for
* Multiple DBs
* Spikes with pattern
* Db don’t’ spike in
parallel

15. Configuring Elastic Pool with Failover Groups
2) Elastic Pool needs to exist on secondary as well
1) Elastic Pool to be created before FG
Delete FG
Delete secondary DB
Create Epool on primary
Import Primary DB into Epool
Create Epool on
Secondary
Configure FG

16. References
SQL Azure Database Pricing - database/
Failover Groups - us/azure/sql-database/sql-database-geo-replication- overview
database/sql-database-designing-cloud-solutions-for- disaster-recovery
database/sql-database-disaster-recovery-strategies- for-applications-with-elastic-pool
database/sql-database-business-continuity