Time To Move From zAAPs to zIIPs?

(Originally posted 2012-09-19.)

Prompted by Troy Coleman’s article zEC12 and zIIP Processors I thought I’d write about how I see the future for zAAPs.

First, his article does a good job of covering the area. So I recommend you read it.

Troy mentions the “zAAP on zIIP” function – which allows zAAP-eligible work to run on a zIIP. It’s not news and it’s a good piece of function: It means you can fill zIIPs more readily, making them a better financial proposition than if zAAP-eligible work had to stay on zAAPs, segregated from zIIP-eligible work. The value of this will depend on which of the following three categories your systems are in:

1. Mostly zIIP-eligible work.
2. Mostly zAAP-eligible work.
3. A mixture of both.

I see customers in all three categories. Strictly speaking I should say “systems in all three categories” as this is an LPAR-by-LPAR and machine-by-machine thing. So, to evaluate its applicability you need to use the usual methods (and apply some of the thinking in zIIP / zAAP Capacity Planning).

Troy also quotes the IBM Statement of Direction on the planned relaxation on the use of zAAP-on-zIIP:

IBM plans to provide a PTF for APAR OA38829 on z/OS V1.12 and V1.13 in September 2012 to remove the restriction that prevents zAAP-eligible workloads from running on zIIP processors when a zAAP is installed on the server.

This gives new configuration choices – which ought to be helpful to a number of customers: I can imagine migrations on an LPAR-by-LPAR basis to zAAP-on-zIIP.

He also mentions the Statement of Direction that:

IBM zEnterprise EC12 is planned to be the last high-end System z server to offer support for zAAP specialty engine processors.

So there’s an obvious direction of travel here. All these things taken together suggest the zEC12 timeframe would be a good one to migrate to zIIPs in. Actually I see nothing here that suggests you couldn’t do it on a z196 : Each customer will have their own choreography.

One final thing to watch out for: The configuration rules haven’t changed in that it’s still only one zIIP per GCP (General Purpose CP) and only one zAAP per GCP. There will be relatively few customers who need more zIIP engines on a machine than GCP engines (even with zAAP-eligible workload running on the zIIPs) but I’m sure they do exist. In those cases careful evaluation (particularly of the financial kind) will be the order of the day. And that’s where Capacity Planning, mentioned in my referenced post, comes in.