Hi @Salves ,
I read that when my disk is managed Azure will automatically change my disk according to its space usage.
1 - Is this true?
Managed Disks = are managed by Microsoft Azure and you don't need any storage account while created new disk. Since the storage account is managed by Azure you do not have full control of the disks that are being created.
Un-managed Disks = are something which requires you to create a storage account before you create any new disk. Since, the storage account is created and owned by you, you have full control over all the data that is present on your storage account. Additionally, you also need to take care of encryption, data recovery plans etc.
There's a good comparison on the blog post over here:
https://buildwindows.wordpress.com/2017/05/31/azure-managed-vs-unmanaged-disks-the-choice/
2 - To change the disk, the VM needs to be deallocated, in which case my VM will be inoperable when this change occurs?
If you want to update the storage type of your managed disk, the Azure VM needs to be deallocated.
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Best regards,
Leon