Limits of Proxmox VE HA retry handling for in-flight VM writes

The goal is to determine whether Proxmox VE’s HA manager can safely retry a failed VM resource without causing duplicate writes to shared storage when the original node loses contact.

Current documentation shows that HA stops the failed resource before relocation and relies on the storage layer for consistency, but it does not provide an idempotent retry mechanism for in‑flight disk writes. The safety of a retry therefore depends on fencing effectiveness, quorum state, and the guest’s ability to recover from incomplete I/O.

• Does HA guarantee exactly‑once write semantics for a VM after a node failure, or can a retry lead to duplicate writes?
• What verification steps can confirm that no duplicate VM instances start on the same shared‑storage disk during a failover scenario?
• How does the reliability of fencing and quorum configuration affect the possibility of unsafe retries?