Proxmox VE HA Cluster & Ceph Calculator
Work out per-node RAM, Ceph memory overhead, corosync vote quorum and cluster link count from the figures Proxmox documents, before the hardware is bought.
How the RAM figure is built. 2 GB for the operating system and Proxmox VE services, plus 8 GB of configured memory per virtual machine spread across the nodes, plus storage overhead. Storage overhead is the larger of 1 GB per TB of used Ceph or ZFS capacity and roughly 8 GiB per OSD daemon, because a rebalancing OSD needs far more than a steady-state one. The per-VM figure is a fixed 8 GB assumption, so model a lighter or heavier guest mix by entering the VM count that carries the same total.
Quorum. A cluster stays authoritative while a majority of votes is present, so the threshold is half the node count rounded down, plus one. Three nodes is the smallest count that survives losing one.
Links. Kronosnet supports up to eight corosync links, and the administration guide warns that a single link backed by a bond can be problematic in certain failure scenarios.
Figures from the Proxmox VE system requirements, the hyper-converged Ceph chapter and the cluster manager chapter. Continue with planning cluster storage and recovery capacity, including the resources needed on surviving nodes.