Merge pull request #293276 from johndowns/reliability-az-latency

[WIP] Reliability Hub - Add inter-zone latency description

Author: prmerger-automator[bot]

articles/reliability/availability-zones-overview.md

@@ -4,21 +4,19 @@ description: Learn about availability zones and how to use them to design resili
 ms.service: azure
 ms.subservice: azure-availability-zones
 ms.topic: conceptual
-ms.date: 01/29/2025
+ms.date: 02/10/2025
 ms.author: anaharris
 author: anaharris-ms
 ms.custom: references_regions, subject-reliability, ai-video-concept
 ---
 
 # What are availability zones?
 
-
 >[!VIDEO https://learn-video.azurefd.net/vod/player?id=d36b5b2d-8bd2-43df-a796-b0c77b2f82fc]
 
-
 Many [Azure regions](./regions-overview.md) provide *availability zones*, which are separated groups of datacenters within a region. Each availability zone has independent power, cooling, and networking infrastructure, so that if one zone experiences an outage, then regional services, capacity, and high availability are supported by the remaining zones. 
 
-Availability zones are connected by a high-performance network with a round-trip latency of less than approximately 2 ms. They are close enough to have low-latency connections to other availability zones, but are far enough apart to reduce the possibility of more than one being affected by a localized outage, such as a power failure or a storm. 
+Availability zones are typically separated by several kilometers, and usually are within 100 kilometers. This distance means they're close enough to have low-latency connections to other availability zones through a high-performance network. However, they're far enough apart to reduce the likelihood that more than one will be affected by local outages or weather.
 
 Datacenter locations are selected by using rigorous vulnerability risk assessment criteria. This process identifies all significant datacenter-specific risks and considers shared risks between availability zones.
 
@@ -82,6 +80,15 @@ $locations = ($response.Content | ConvertFrom-Json).value
 
 For each region, Microsoft aims to deploy updates to Azure services within a single availability zone at a time. This approach reduces the impact that updates might have on an active workload, allowing the workload to continue to run in other zones while the update is in process. To take advantage of sequenced zone updates, your workload must be already configured to run across multiple zones. For more information about how Azure deploys updates, see [Advancing safe deployment practices](https://azure.microsoft.com/blog/advancing-safe-deployment-practices/).
 
+## Inter-zone latency
+
+Within each region, availability zones are connected through a high-performance network. Microsoft strives to achieve an inter-zone communication with round-trip latency of less than approximately 2 milliseconds. Low latency allows for high-performance communication within a region, and for synchronous replication of data across multiple availability zones.
+
+> [!NOTE]
+> The target latency refers to the latency of the network links. Depending on the communication protocol you use and the network hops required for any specific network flow, the latency you observe might be different.
+
+In most workloads, you can distribute components of your solution across availability zones without a noticeable effect on your performance. If you have a workload with a high degree of sensitivity to inter-zone latency, it's important to test the latency between your selected availability zones with your actual protocols and configuration. To reduce inter-zone traffic, it's possible to use [zonal deployments](#zonal-and-zone-redundant-services), but optimally, you should use multiple availability zones in your reliability strategy plan. 
+
 ## Availability zone architectural guidance
 
 To achieve reliable workloads: