Setting disk size when migrating from unmanaged disk to managed disk.

Question

Setting disk size when migrating from unmanaged disk to managed disk.

Kyle James 0

We have a 1023 GiB unmanaged disk attached to a 2012 Windows R2 datacenter VM, and it must be migrated to a managed disk. Since we are only using ~20GB of that disk, is there a way to specify that the new managed disk should be 128GB instead of an entire terabyte?

Keshavulu Dasari 4,840 Reputation points Microsoft External Staff Moderator

2025-06-02T16:30:27.96+00:00

Hi Kyle James

When migrating from an unmanaged disk to a managed disk in Azure, the managed disk will, by default, be created with the same size as the source unmanaged disk, if you are only using 20 GB of the 1023 GiB disk, and you want to reduce the size of the managed disk to something like 128 GB, you can do this but not directly during the migration.

For more information:

https://learn.microsoft.com/en-us/azure/virtual-machines/windows/convert-unmanaged-to-managed-disks

https://learn.microsoft.com/en-us/azure/virtual-machines/unmanaged-disks-deprecation

Please let me know if you have any quires or Steps to Reduce Disk Size During Migration, I am glade to assist.
Keshavulu Dasari 4,840 Reputation points Microsoft External Staff Moderator

2025-06-03T16:05:19.7966667+00:00

Hi Kyle James,

Please let me know if you have any quires or Steps to Reduce Disk Size During Migration, I am glade to assist.
Keshavulu Dasari 4,840 Reputation points Microsoft External Staff Moderator

2025-06-04T18:00:02.09+00:00

Hi Kyle James,

Just checking in to see if the response helped. If you have any questions, let me know in the "comments" and I would be glad to assist you.
Hari Babu Vattepally 3,270 Reputation points Microsoft External Staff Moderator

2025-06-04T18:55:40.9+00:00

Hi @Kyle James,

Following up to see if the above answer was helpful. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Your answer

Keshavulu Dasari 4,840 Reputation points Microsoft External Staff Moderator

2025-06-02T16:30:27.96+00:00

Hi Kyle James

When migrating from an unmanaged disk to a managed disk in Azure, the managed disk will, by default, be created with the same size as the source unmanaged disk, if you are only using 20 GB of the 1023 GiB disk, and you want to reduce the size of the managed disk to something like 128 GB, you can do this but not directly during the migration.

For more information:

https://learn.microsoft.com/en-us/azure/virtual-machines/windows/convert-unmanaged-to-managed-disks

https://learn.microsoft.com/en-us/azure/virtual-machines/unmanaged-disks-deprecation

Please let me know if you have any quires or Steps to Reduce Disk Size During Migration, I am glade to assist.
Keshavulu Dasari 4,840 Reputation points Microsoft External Staff Moderator

2025-06-03T16:05:19.7966667+00:00

Hi Kyle James,

Please let me know if you have any quires or Steps to Reduce Disk Size During Migration, I am glade to assist.
Keshavulu Dasari 4,840 Reputation points Microsoft External Staff Moderator

2025-06-04T18:00:02.09+00:00

Hi Kyle James,

Just checking in to see if the response helped. If you have any questions, let me know in the "comments" and I would be glad to assist you.
Hari Babu Vattepally 3,270 Reputation points Microsoft External Staff Moderator

2025-06-04T18:55:40.9+00:00

Hi @Kyle James,

Following up to see if the above answer was helpful. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

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Setting disk size when migrating from unmanaged disk to managed disk.

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