# Account for cache misses against both Azure VM storage limits

> Why can a host-cached disk's read workload still consume a VM's uncached storage allowance?

- Canonical URL: https://update.dsesecurity.com/updates/dse-20260909-057-account-for-cache-misses-against-both-azure-vm-storage-limits/
- Publisher: Detection Systems & Engineering (DSE Security)
- Author: DSE Security Editorial Team
- Published: 2026-09-10T00:30:59+00:00
- Modified: 2026-09-10T00:35:07+00:00
- Last reviewed by DSE: 2026-09-09
- Resource type: Explainer
- DSE priority: Information
- Topics: IT
- Reading time: 2 minutes

## What you need to know

Why can a host-cached disk's read workload still consume a VM's uncached storage allowance?

## Potentially affected

Azure VMs and managed disks supporting premium-storage host caching, with the actual cache mode identified.

## DSE recommendation

Map the measured read path before deciding which storage limit needs attention.

## Article

## Source facts

Azure VMs with premium storage and host caching have separate cached and uncached storage limits. A read satisfied by host cache counts against the cached limit. A cache miss must reach the disk and counts against both cached and uncached VM limits. Attached disks also have their own IOPS and throughput limits. Enabling caching therefore does not make every read independent of the remote disk path. [Microsoft Learn](https://learn.microsoft.com/en-us/azure/virtual-machines/disks-performance).

## Applicability

Use this distinction when a read-heavy workload has host caching enabled but still appears constrained by uncached storage. Identify the VM size, disk configuration, actual cache mode, and whether the observed workload is reading data already present in cache.

## DSE recommendation

Map the measured read path before deciding which storage limit needs attention. Ask the performance owner to distinguish cache-hit and cache-miss behavior and compare VM-level evidence with the affected disks. Keep observations from an already warmed workload separate from first-read behavior. Do not assume a higher disk tier or a cache setting alone resolves an unexplained limit.

## Verification

Use a representative nonproduction workload to compare the relevant VM and disk metrics under controlled read conditions. Record the workload shape, cache configuration, measured latency, and which limit approaches saturation. Change one relevant condition at a time and compare results with the proposed explanation. If the observed bottleneck moves between cached and uncached paths, preserve that finding rather than combining the results into one unexplained throughput number.

## Official references

[Microsoft Learn: Virtual machine and disk performance](https://learn.microsoft.com/en-us/azure/virtual-machines/disks-performance). Source reviewed September 9, 2026.

## Primary reference

- Name: Virtual machine and disk performance - Azure Virtual Machines | Microsoft Learn
- Authority: Microsoft Learn
- URL: https://learn.microsoft.com/en-us/azure/virtual-machines/disks-performance
- Source publication date: Not stated by the source

## Citation and use

Preferred citation: “Account for cache misses against both Azure VM storage limits,” DSE Security, https://update.dsesecurity.com/updates/dse-20260909-057-account-for-cache-misses-against-both-azure-vm-storage-limits/
Publishing principles: https://update.dsesecurity.com/updates/dse-updates-editorial-methodology/
Usage and citation policy: https://update.dsesecurity.com/usage/
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