Many users are already aware of how to configure CPU and memory resources for VMs under AHV. However, many users are unaware that these resources can be added even while a VM is running or powered-on. This feature can be particularly useful when an already-running VM is reaching CPU or memory exhaustion and needs to remain online while critical workloads are being processed.
However and, different from adding resources while a VM is powered-down, there are some limitations to be aware of:
Only additional vCPU sockets (not cores) can added
The multi-queue storage controller will not dynamically create any additional queues if additional CPU sockets are added
The amount of memory that can be added is limited to what is currently available on the specific AHV host which is currently hosting the VM
The amount of times that memory can be added while a VM is running is limited to two or three
According to the above limitations, it may be best to limit the use of this feature to explicitly needed situations and to attempt to size the VM resources appropriately before power-on. You can find more information regarding this feature within the HotPlug CPU and Memory section of the AHV Best Practice Guide as well as the Managing a VM (AHV) section of the Prism Web Console Guide.