Shared storage is not absolutely necessary in a Proxmox cluster environment, but without a doubt, it makes storage management a simpler task. In a small business environment, it may be fine not to have 24/7 uptime and 100% reliability, so a local storage system will suffice. When data grows beyond several terabytes, it may or may not fully justify shared storage. The question is how important is budget, reliability, resiliency, and accessibility. In most enterprise virtual environments with critical data, shared storage is the only logical choice due to the benefits it brings to the whole cluster operation. The following are considered benefits of using shared storage:
Live migration of a virtual machine
Seamless expansion of multinode storage space
Centralized backup
Multilevel data tiering
Central storage management
