What are the different methods to reduce the size of an Azure VM’s OS disk?

Question

I have create Azure VM with windows server 2022 + SQL Web image. While creating it did not gave me option to select OS disk size. By default it was 128 GB. Out of which I need max 30-40 GB. SO 64 GB size is enough for me. Azure Portal is not allowing to change size to lower size. The cost is almost 50% more that what I required.
What is the other way to reduce disk size while keeping the windows server 2022 + SQL Web image as is?

Answer 1

Hello Kunal.

Thank you for your question. I understand the concern around cost optimization when the Azure Marketplace image (Windows Server 2022 + SQL Web) provisions a 128 GB OS disk by default, even though your actual usage is much lower.

Why the Azure portal blocks reducing OS disk size

Azure does not support shrinking an OS disk in place. Managed disks—especially OS disks—can only be expanded, not reduced, to prevent data corruption or boot issues. This is expected behavior, and the Azure portal correctly enforces this limitation.

Recreate the VM with a smaller OS disk

The only supported way to truly reduce OS disk size is to create a new VM:

• Use a base Windows Server 2022 image (which allows OS disk size selection)
• Specify a smaller OS disk (e.g., 64 GB) at creation time
• Install SQL Server Web manually
• Migrate databases and application data (preferably on data disks)

This approach is fully supported and avoids risks associated with unsupported disk manipulation.

Use a custom image

If you want to keep the same configuration:

• Generalize (Sysprep) the VM
• Capture a custom image
• Deploy a new VM from that image and choose a smaller OS disk, if the image supports it.

Optimize data placement (Best practice for SQL workloads)

While the OS disk can’t be reduced:

• Move SQL data, logs, and backups to separate data disks
• Right‑size data disks based on actual usage
• For data disks, the supported way to reduce size is to create a smaller disk, migrate data, and delete the larger disk

This pattern is officially documented and supported for data disks.

Reducing or shrinking an Azure VM OS disk is not supported and may result in data loss or an unsupported configuration. Always ensure backups are in place before any disk or VM re‑creation activities.

If the issue persists or you’d like guidance on recreating the VM or migrating SQL workloads safely, please comment in the Comment section, and we’ll be happy to assist further and respond promptly.

Thanks,
Manish.

Answer 2

Hello @Kunal Chiddarwar,

To reduce the disk size of your Azure VM with Windows Server 2022 and SQL Web image, you cannot directly downsize the OS disk due to the risk of data loss. Instead, you can create a new, smaller data disk, copy the data from the original disk to the new one, and then delete the old disk. This method allows you to effectively manage your storage without losing data.

Additionally, it’s important to assign disk sizes based on actual requirements rather than over-provisioning. You can always expand data drives later without downtime, which helps in optimizing costs.

Consider using the Azure portal to manage your disks effectively, ensuring you select the appropriate size and performance tier for your needs.

Decrease the size of an Azure data disk without losing data

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