Innsbruck z/OS and Storage Conference – Day 4

(Originally posted 2005-04-14.)

Session TSP11: Performance of the TotalStorage DS8000, Speaker: Lee La Frese

Of course a new disk controller from IBM is going to appear awesome. 🙂 DS8000 is no exception.

Currently 2-way and 4-way POWER5 processors. Statement of Direction for an 8-way machine. POWER5 can go up to a 64-way.

I/O access density has levelled out over the last five years (2000 to 2005), having historically decreased (over the 1980 to 2000 period).

There’s a new adaptive cacheing algorithm (called ARC). Very effective at low hit ratios (for Open). Likely to have less benefit at higher cache hit ratios (eg z/OS workloads).

A small number of customers in the room have FICON Express2. There is a paper from Poughkeepsie on this.

Channel Measurement Block granularity has recently decreased from 128us to 5us. Which actually has been known to cause an increase in response times reported by RMF. But this doesn’t affect Lee’s performance numbers which come from the controller itself and aren’t subject to mainframe processor considerations.

PPRC (Sync Remote Copy) performance has improved dramatically. The big reductions were in ESS. But a 0.38ms cost for DS8000 over 8KM has been measured. This is not really showing what happens at distance. 303km distance showed as about 4ms and 0km as about 0.5ms. Lee noted that you could interpolate reasonably well as the elongation with distance is pretty much linear. The above numbers are at low load. Load doesn’t alter the picture very much – until you hit the knee of the curve.

Session Z16: Sharing Resources in a Parallel Sysplex, Speaker: Joan Kelley

Actually this was rather more about CF performance than actual resources. But it was very useful nonetheless.

Joan talked about shared CFs. Her “classic” scenario is a “Test” CF whose performance is not important sharing with a “Prod” CF where is important. Recall: each CF needs its own Receiver links – so need to configure accordingly.

Delayed requests can even break Duplexing – as a consequence of timing out a request.

Dynamic Dispatch puts the CF to sleep for 20ms at low utilisations, less time for higher utilisations.

A good design point for this sharing case is to turn Dynamic Dispatch on for “Test” and off for “Prod”. (D DYNDISP shows whether Dynamic Dispatch is on for a CF. (Obviously you can also infer that from RMF as well.))

She had a good foil on responsiveness for different “Test”/”Prod” LPAR weight regimes. It showed that at low Test request rates the weights don’t matter much. At higher rates, though, weights of eg 5/95 produce much better responsiveness than eg 30/70. With System-Managed Duplexing you should set weights so that the Prod (duplexed) CF is dispatched 95% of the time – to avoid the timeouts I mentioned earlier.

With Dynamic ICF Expansion the CF can expand to additionally use a shared engine. If the shared engine is totally available – i.e no other LPAR wants it – the performance is close to that additional engine being dedicated.

Because ICF engines, IFL engines and IFA/zAAP engines share the same pool it is possible for an IFL or IFA to acquire cycles at the expense of the ICF LPARs.

There were several foils on CF links. I’m going to have to learn up on this as well: It’s got a lot more complicated. 🙂

Session ZP12: DB2 Memory Management in a 64-Bit World, Speaker: Me

This went reasonably well. I did get one question which was about what value to set MEMLIMIT at (which I think translates into what REGION value to have for the DBM1 address space). At present the answer has to be “I don’t know.” 😦 That’s because I don’t know if Extended High Private users can expand down into memory below the REGION value. If that makes any kind of sense. 🙂 I clearly need to research how REGION interacts with Extended High Private (which is what DB2 uses – mainly).

Session Z20: What’s New in DFSORT?, Speaker:Me

A small but reasonably engaged audience. One good question was essentially “if I’ve set my DFSORT parameters in particular ways years ago which do I need to change now?” Basically it would take a review of the parameters but most of them wouldn’t need to change. But some of newer ones are worth looking at to see how helpful they could be.

Published by Martin Packer

I'm a mainframe performance guy and have been for the past 35 years. But I play with lots of other technologies as well.

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