Edit: Some links no longer work.
Originally posted February 13, 2013 on AIXchange
Recently I was brought into a large migration project that was already underway. An outside team had done the design, and the goal of these folks was to create a system that emphasized simplicity. To make it easy to manage, they decided that the system wouldn’t have virtualization or allow the sharing of resources. Each LPAR would have dedicated adapters and dedicated CPUs.
It’s been some time since I’ve seen large systems designed and set up like this. I will admit that, with non-virtualized systems, determining which card belongs to which LPAR is a snap.
Of course there were still challenges. As the system was being set up, the decision was made to install IBM Systems Director on one of the NIM LPARs. This immediately raised a red flag in my mind, because I recall a Nigel Griffiths presentation where he said — and I paraphrase — oh no, never, ever, ever, ever install a NIM server and Systems Director together on the same LPAR running AIX. Really he probably just said this isn’t a good idea.
So I contacted Nigel, and my questions and his responses became the subject of this blog post:
“I have cut down the questions a bit but it is two parts: His customer is thinking about putting Systems Director on to their NIM server. Rob remembered me commenting on this but wants the details. They are planning to give it one dedicated POWER7 core and 12G memory. What do I think about that?
“Two years ago this combination (NIM & ISD) was not allowed (I think it was just not tested so not supported rather than it being a problem), but now is OK. So you can find older [web] pages with duff info.
“However, I do NOT recommend it. To get NIM to push out the very latest AIX version, the NIM server needs to be at that AIX level. But Systems Director may not be supported at that very new AIX level. Then you can’t get Systems Director support. This is a ‘will probably work but not supported’ risk that you have to decide [whether to take].
“Running a single dedicated CPU… will make Systems Director look and feel slow. With a dozen users the CPU use will go up and be a lot more peaky. With NIM it would not matter but Systems Director GUI would suffer and so would the user. Personally a dedicated CPU for NIM is pretty dumb — that CPU could be used elsewhere most of the time.”
I agree. A dedicated CPU is dumb when you could use dedicated donating or shared processor pools. However, in this case, I wasn’t involved in the design of the server. I was only asked by the customer if I could make it work.
My gut feeling was that mixing these workloads was a bad idea, and mixing them on only one dedicated core made it even worse. I certainly understand the customer not blindly taking me at my word, so that’s why I brought in the big guns — i.e., Nigel. Between his presentations, his videos and his all-around Power Systems knowledge, I knew he was the right person to ask. And I’m grateful for his fast response.
No matter how experienced and accomplished you are, it never hurts to have someone you can go to who can give you an answer or validate your own course of action. Who do you have in your corner when you get stuck?