Question. In vSphere 4.1 there’s a limit of 8 virtual cores per guest. If the host has 24 cores available – and I have only one other Virtual Machine(VM) using 8 virtual cores – how can I utilise the remaining 8 cores?.
Host – 24 cores
VM1 – 8 Cores
VM2 - 8 cores
Answer 8 virtual cores means you’ll never have more than 8 threads executing in parallel on the VM.
vSphere uses a queue structure for CPU resources, dispatching work to processors as required. Once the work is processed , it’s reassembled and returned to the vCPU. ESX does the work of reassembling the multiple work units.
DBA perspective – highly iterative and closely aligned tasks are suited to this architecture. Application architecture examples include Process Servers.
Queries requiring complex instruction sets with high levels of earlier instruction dependancy are not as suited.
The DBA must answer the question Is Virtualization a viable alternative?
The main difference between UNIX and ESX CPU Schedulers is how processor priority is decided. In UNIX , it’s based on user choice. In ESX, the decision is based on actual usage and “entitlement” , such as reservation, shares and limit