There are three stages of a .vhd file or a PVM disk:
- raw .vhd file in blob storage (use any blob explore tool to manage this)
- .vhd files recognized by PVM as disks (use Azure portal to create/delete disk)
- PVM disk attached to a PVM instance (use Azure portal to attach/detach disk)
O/S disk vs. Data disk: this is decided when you recognize a raw blob file as a disk. O/S disk can be used to create a VM instance.
Image vs. Disk: Image is "sysprepared" O/S disk. You can use either Image or O/S Disk to create a VM instance. If you use O/S Disk, all the old user name, machine name etc. persist, while everything is as from scratch if you use Image.