Follow these steps to request manged disk quota increase from Azure Portal:
- From the Azure portal, select Quotas and then select Compute.
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Locate the subscription, region, managed disk type for which you want to increase your manged disk quota. Then select "Create new support request" icon.
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In the New support request, select Quota type: "Storage: Managed Disks Limits".
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In the Additional details dialog, select the requests details, enter the new limit, then select the region.
For more information visit Azure Quota Documentation.