over-provisioning ratio
also: resource oversubscription, virtual-to-physical ratio, subscription ratio
The ratio of allocated virtual resources to physical resources in a virtualized or cloud environment, allowing multiple virtual machines to share underlying hardware capacity.
Over-provisioning ratio measures how many times more resources are allocated to virtual machines than physically available. For example, a ratio of 4:1 means 4 GB of virtual RAM is allocated for every 1 GB of physical RAM, betting that not all VMs will use their full allocation simultaneously.
This practice works because most workloads don't use peak resources continuously. A web server might allocate 8 GB of RAM per VM but typically use only 2-3 GB, allowing a physical server with 16 GB to safely host 8 virtual machines.
Higher ratios increase efficiency and cost savings but risk performance degradation if too many VMs demand resources at once. Linux hypervisors like KVM and management tools like libvirt balance this trade-off through memory ballooning, swapping, and CPU scheduling to maintain performance while maximizing resource utilization.