Today we’re sharing the public preview of per disk metrics for all Managed & Unmanaged Disks. This enables you to closely monitor and make the right disk selection to suit your application usage pattern. You can also use it to create alerts, diagnosis, and build automation.
Prior to this, you could get the aggregate metrics for all the disks attached to the virtual machine (VM), which provided limited insights into the performance characteristics of your application, especially if your workload is not evenly distributed across all attached disks. With this release, it is now very easy to drill down to a specific disk and figure out the performance characteristics of your workload.
Read about it in the Azure blog.