After creating an Azure Virtual Machine (VM), you may wish to add one or more disks. Maybe you want to increase your VM's storage; capacity or maybe you want to separate some data from the operating system disk. Either way, open your Virtual Machine properties in the Azure Portal and select "Disks", as shown in Fig. 1.
The Disks blade displays, as shown in Fig. 2.
Under the "Data Disks" section, click the "Name" dropdown of the first empty line; and select "Create Disk", as shown in Fig. 3.
The "Create Managed Disk" blade displays (Fig. 4).
Provide a disk name, resource group, region, type, and size. I generally prefer to create a disk in the same resource group and region as the VM. You can create a new empty disk, or one based on an existing snapshot.
Click the "Create" button to begin creating the disk, which will take a few minutes.
When finished, you should see your new disk listed in the VMs' Disks blade, as shown in Fig. 5.
Repeat this process to add any more disks you like.
When you connect to the VM (via Remote Desktop for a Windows VM and via SSH for a Linux VM), you will see the extra disk and you will be able to read to and write from this disk.