# Reconcile physical zones before using a shared capacity reservation

> Why can matching zone numbers in two subscriptions still select different physical locations for shared reserved capacity?

- Canonical URL: https://update.dsesecurity.com/updates/dse-20260909-032-reconcile-physical-zones-before-using-a-shared-capacity-reservation/
- Publisher: Detection Systems & Engineering (DSE Security)
- Author: DSE Security Editorial Team
- Published: 2026-09-10T00:31:24+00:00
- Modified: 2026-09-10T00:32:00+00:00
- Last reviewed by DSE: 2026-09-09
- Resource type: Guide
- DSE priority: Information
- Topics: IT, Networks & Infrastructure
- Reading time: 2 minutes

## What you need to know

Why can matching zone numbers in two subscriptions still select different physical locations for shared reserved capacity?

## Potentially affected

Teams evaluating preview sharing of zonal Azure capacity reservation groups across subscriptions.

## DSE recommendation

Build a provider-to-consumer zone mapping for the selected shared reservation before approving a deployment.

## Article

## Source facts

Sharing Azure capacity reservation groups across subscriptions is preview. Availability-zone numbers are logical labels with subscription-specific physical mappings, so equal labels need not identify the same location. Microsoft requires zone remapping when deploying through a shared zonal reservation group. The provider and consumer subscriptions each need their own applicable quota. [Microsoft Learn](https://learn.microsoft.com/en-us/azure/virtual-machines/capacity-reservation-group-share).

## Applicability

Scope the review to a named provider subscription, consumer subscription, region, and shared reservation. Record both subscriptions’ actual zone mappings rather than transplanting the documentation’s illustrative zone numbers. Check the documented sharing permissions and preview limitations before planning an operational trial.

## DSE recommendation

Build a provider-to-consumer zone mapping for the selected shared reservation before approving a deployment. Have both subscription owners review the physical location behind the requested consumer zone and the reservation’s provider-side label. Include independent quota checks in that review. Keep the mapping with the deployment parameters so a later operator does not replace it with an apparently simpler same-number choice.

## Verification

In an approved preview trial, compare the requested zone, resolved physical mapping, reservation identifier, and resulting VM placement. Ask a second operator to reconstruct the mapping from the retained evidence. Investigate a mismatch before changing unrelated VM settings or requesting more capacity. Record the two subscription identifiers explicitly; a successful deployment from one consumer is not the acceptance result for another consumer’s mapping.

## Official references

[Microsoft Learn: Share a Capacity Reservation Group in Azure](https://learn.microsoft.com/en-us/azure/virtual-machines/capacity-reservation-group-share). Source reviewed September 9, 2026.

## Primary reference

- Name: Share a Capacity Reservation Group in Azure - Azure Virtual Machines | Microsoft Learn
- Authority: Microsoft Learn
- URL: https://learn.microsoft.com/en-us/azure/virtual-machines/capacity-reservation-group-share
- Source publication date: Not stated by the source

## Citation and use

Preferred citation: “Reconcile physical zones before using a shared capacity reservation,” DSE Security, https://update.dsesecurity.com/updates/dse-20260909-032-reconcile-physical-zones-before-using-a-shared-capacity-reservation/
Publishing principles: https://update.dsesecurity.com/updates/dse-updates-editorial-methodology/
Usage and citation policy: https://update.dsesecurity.com/usage/
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