Microsoft Azure storage accounts come in two varieties.
Blob storage is specifically for “unstructured data”, which ultimately means it’s a sort of file share, and much more massively scalable. This storage type, however, is not optimized for virtual machine disks and, contrasted with a general purpose storage account, cannot have SSD storage (“Premium performance”) selected.
As specified in the Veeam Backup & Replication User Guide:
The list of storage accounts contains only general purpose storage accounts. Blob storage accounts are not displayed in the list of subscriptions. For more information about account types, see Microsoft Docs.
If you select a premium storage account, ensure that the restored workload size is compatible with the selected account.
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