Availability zones

In the Ultra Transcenders books

AZ-305AZ-104AZ-700AZ-900AZ-802ALZ

Each book explains Availability zones in context, with comparison tables and the common traps.

Terms in this definition

• Physical

  Describes the concrete, real-world parts that put a logical architecture into effect.

• Datacenter

  A building packed with racked servers that has its own electricity supply, cooling and network links. Microsoft gathers these buildings into Azure regions, and as a customer you pick the region, never which building your resources land in.

• region

  A provider-defined grouping in VCF Automation of Supervisors that all share one NSX Local Manager; tenants consume its compute, storage and memory via quotas set per region.

• Virtual machines

  Infrastructure-as-a-service compute giving complete control of the operating system, making it a fit for lift-and-shift moves and for software relying on OS-level pieces like COM.

• LEAST

  Pass up to 254 expressions to this T-SQL function and it hands back whichever is smallest. Both Fabric Warehouse and SQL analytics endpoints support it.

• SLA

  A commitment to a level of uptime, such as 99.99% for VMs spread over availability zones, 99.95% for an availability set and 99.9% for one VM.

Related terms

• AZ SKU

  Any VPN or ExpressRoute gateway SKU carrying the AZ suffix (VpnGw1AZ to 5AZ, ErGw1Az to 3Az). In regions with availability zones its instances spread across zones; in other regions it deploys regionally, becoming zone-redundant once zones are introduced there.

• Billing zone

  A group of Azure regions sharing one price for outbound data transfer. Despite the name it is unrelated to availability zones, which are physically separate datacentre groups within a single region.

• ErGw1Az

  ExpressRoute gateway SKU deployed across availability zones, offering roughly 1 Gbps like Standard, without FastPath support.

• Flexible orchestration

  The scale set mode Microsoft recommends. Standard Azure VMs of different types can be combined, distributed over fault domains or availability zones, with up to 1,000 instances in total.

• GZRS

  Geo-zone-redundant storage. Writes go synchronously to at least three availability zones in the primary region, as ZRS does, and are later copied asynchronously to a secondary region that keeps LRS copies. With RA-GZRS that secondary can also be read.

• Peering location

  Where, physically, an ExpressRoute circuit meets the Microsoft edge. Circuits cannot be pinned to availability zones, so stacking several at one location adds no zone resilience.

• Premium SSD ZRS

  Variant of Premium SSD that writes synchronously to three availability zones so the disk survives the loss of a datacentre. Ultra Disk and Premium SSD v2 do not offer it.

• VNet

  A private network belonging to a single subscription and region and covering all of that region's availability zones. A VM can only use a VNet located in the same region.