Re: Memory and CPU Considerations for IBM i LPARs

[Rob Berendt <robertowenberendt@xxxxxxxxx>]

There is a vendor tool which you let run for awhile and then it offers
suggestions.  I forget the name off of the top of my head and I have a web
meeting coming up.  My BP has permission to load it temporarily for such
system evaluations.
I have a few very limited use lpars running .15 to .2 cpu on a 9105-41B
Our most CPU lpar is our main ERP at 4 processors on a 9105-42A.  It peaked
out way off hours at 50% utilization.  Must be some bodacious batch jobs.
During work hours it stayed under 30% utilization for a vast majority of
the time.

Hey, that software might be from Midrange Performance Group.
Gotta go.


On Wed, Aug 21, 2024 at 5:08 PM Jacob Banda via MIDRANGE-L <
midrange-l@xxxxxxxxxxxxxxxxxx> wrote:

> So I have a new Power 10 set up with IBM i hosting i and Linux partitions,
> managed with V10R3 vHMC. I have a good understanding of the workings of
> Processing Units (PU) vs. Virtual Processor (vCPU) allotments in the
> partition profiles and have been monitoring the workloads with the HMC
> Performance Dashboard for Average and Maximum CPU consumption.
>
> My questions are regarding assigning sufficient CPU resources to the client
> partitions and identifying memory usage in the IBM i client partitions.
>
> 1. How the heck do I identify just how much memory is required for my
> workloads in an IBM i partition? DSPSYSSTS just seems to dump the total
> system main storage (memory), but I have a feeling that it's allocating
> everything because we gave it a lot to begin with. How can I identify how
> much I can cut back? I would REALLY like to cut back some memory on
> partitions that we migrated from dedicated boxes with only 1 partition per
> box.
>
> 2. Is there a rule of thumb for the PU to vCPU ratio on Power hardware? On
> my x86 hosts I tend to shoot for 1:2. For mostly idle workloads, I use 1:4.
>
> 3. For Shared Processor Partitions, do you all try to set Entitled Capacity
> (PU) to be close to average usage, and vCPU to peak usage, with the MAX PU
> value set to match the vCPU max, or as close as possible? I read this on a
> slidedeck published by Bjorn Roden during an IBM Edge 2015 conference.
>
> Thanks,
>
> -------------
> Jacob
> -------------
>
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