Difference between Managed and Unmanaged Disk
I would like to highlight some of the benefits of using managed disks:
Simple and scalable VM deployment: Managed Disks will allow you to create up to 10,000 VM disks in a subscription, which will enable you to create thousands of VMs in a single subscription.
Better reliability for Availability Sets: Managed Disks provides better reliability for Availability Sets by ensuring that the disks of VMs in an Availability Set are sufficiently isolated from each other to avoid single points of failure.
Highly durable and available.
Granular access control: You can use Azure Role-Based Access Control (RBAC) to assign specific permissions for a managed disk to one or more users. Managed Disks exposes a variety of operations, including read, write (create/update), delete, and retrieving a shared access signature (SAS) URI for the disk.
Azure Backup service support: Use Azure Backup service with Managed Disks to create a backup job with time-based backups, easy VM restoration and backup retention policies.
Are unmanaged disks still supported: Yes. Both support unmanaged and managed disks. We recommend that you use managed disks for new workloads and migrate your current workloads to managed disks.
Refer Azure Managed Disks Overview for more details.
Managed and unmanaged drives in Azure are different concept.
Unmanaged approach treat the drive as a service provided under storage account, you can use this "service" connecting it to your VM but from management perspective is completelly different entity. Contrary to this approach managed drive is a HDD you connect to your VM, storage account behind it is managed by Azure, so you should get appropriate performance for your disk size. In fact because VMs have there own IOPS limits associatied with hardware profile size just resizing the disk will generally doesn't provide you better performance. Since managed drives are newer and more "sophisticated" service they are also more expensive.
If you are interested in this topic I did quite complete comparison based on options available over az command line options here. There is also nice practical differences summary here
Essentially, Managed Disks are easier to use because they don't require you to create a storage account. I think Azure still creates one, but this detail is hidden from you.
The benefit of not having to manage a storage account is that storage accounts have limits, like max IOPS, so that if you place too many disks in a storage account, it is possible that you will reach the IOPS limit. Azure takes care of this for you.
If you have VMs in an Availability Set, Azure will make sure that disks are on different "stamps" ensuring that disks are spread out so that you don't have a single point of failure for the disks.
As for a Con, I've encountered two (but there are probably more):
When taking snapshots they are Full Snapshots, not incremental, so this adds to storage cost.
If you are setting up a Disaster Recovery between two Azure regions, using Recovery Services, managed disks are not yet supported.- Managed disk for Azure site recovery is now supported