Implicit Capping for LPARs - a perspective on Virtual Processors
AnthonyEnglish 270000RKFN Visits (8075)
If you mix production and non-prod LPARs on the same managed system, you may be worried that the non-prod LPARs could chew up much-needed production processing juice. What are your options here? Here are some common solutions:
Before looking at the Implicit capping, here are some of my thoughts on the first two options:
Separate shared processor pools
Separate shared processor pools are not available on all systems, And they do also isolate the LPARs to their own shared processor pool, which is (if you'll pardon the momentary escape into a sporting analogy) a bit like a hard wall separating the lanes in a swimming pool. The two pools are separate, which can be a bit restrictive, especially if you're on the crowded side of the wall.
Capping of the non-prod LPARs
This is like a wall in the swimming pool for the non-prod swimmers. The prod swimmers are allowed to swim in and out of the non-prod area, but the non-prod guys have to stay where they are. Good for prod. If you prefer, here's a back yard analogy: you are allowed to wander into your neighbour's yard when you're pressed for space, but your neighbour isn't allowed into yours.
Now the let's see what the Redpiece says about implicit capping.
Implicit capping of non-prod LPARs
First, a word about using DLPAR:
It's good to have the dynamic LPAR option, but as it requires user intervention or at least scheduling of the DLPAR operation (not available on all systems), you're better to leave it to the hypervisor.
So here's the suggestion:
The number of VCPUs [they're referring to Virtual Processors] that are available to a partition limits the number of whole physical CPUs that this LPAR can address, because one virtual CPU represents at maximum one physical CPU. The LPAR is therefore effectively capped at a maximum physical processor utilization that is equal to its number of configured VCPUs.
The configured VCPUs is the entitlement for Virtual Processors.
Here's what they see about the LPAR weight:
The advantage of implicit capping versus explicit capping is:
I'll have to think through this but there's a lot of very helpful information on virtualisation in this SAP Applications on IBM PowerVM Redpiece. It's worth reading even if you're not running SAP systems. Be sure to read the Micropartitioning design option in section 4.2.