Understand Persistant VM disks (1)

Persistent VM (PVM) is Azure's IaaS offering comparable to Amazon's EC2. Unlike EC2 which uses local disks for the majority of the time, PVM uses Azure blob storage to store disks. This design has multiple implications.

On the good side, your data in the disks are more reliable, as every Azure blob automatically has 3 local copies which are always synchronized and another 3 copies in a different data center 100+ miles away which is delay synchronized. On the bad side, the disk I/O performance might be impacted. For this reason, PVM do use both Azure blob backed disks and local only disks to optimize the disk I/O, so it's important to understand where each disk lives. Below is the explanation:

C: disk is the OS disk. Persisted in blob storage.

D: disk is local disk. Not persisted, but very fast.

F: disk is additional user data disk. Persisted in blob.