zEC12 GA2 Group Capping
OzanBaran 120000M0Q0 Visits (5007)
A colleague from the field reached out to me recently with a couple of questions on IRD, Defined and Group Capacity Limits which made me think of a zEC12 GA2 related change so figured if he can benefit from it maybe others could do so here we go ...
First of all WLM Capping is the same thing as Soft Capping and you could say that they are 'implemented' via Defined and/or Group Capacity Limits.
Both Defined Capacity Limit (DCL) as well as the Group Capacity Limit (GCL) are specified in Millions of Service Units (MSU).
While DCL is assigned to a single LPAR, GCL is assigned to a group of LPARs. That means the GCL MSUs are distributed across all the LPARs within that group. This distribution is done based on the LPAR weights.
One of my colleague's questions was, what if I am using IRD LPAR weight management and I reach my Group Capacity Limit and my LPARs are capped... can IRD continue to manage my LPAR weights while the LPARs are capped?
The answer is NO. Currently IRD is not allowed to make any weight changes while capping is in place.
Another question was, 'which' weights do we use for the GCL MSU distribution? Current or Initial LPAR weights? since they can be different, especially when using IRD.
The answer is 'it depends' ... prior to zEC12 GA2 we used to use the current LPAR weights. With zEC12 GA2 -- and SW support -- we use the initial LPAR weights.
Here is a screen shot from a presentation by Horst Sinr
For more details on Defined Capacity and Group Capacity concepts please refer to the following documentation:
z/OS Performance: WLM Soft Capping Support for Sub Capacity Pricing
MVS: Planning: Workload Management
Also note that with z/OS V2R1 you can use Capacity Provisioning Manager for z/OS to manage DCL and GCL based on time and/or workload based policies. You can read more about that in one of my previous blogs: