Zero experience. However, as I was reading this I seem to remember that when IBM announced their first 10-way mainframe that Amdahl released a statement that they would never build a mainframe with more than 8 CPU's. Their reasoning was you had diminishing returns once you went beyond 8 because of the overhead of managing them. In fact I think they stated that at some point that N+1 CPU's would give you less performance than N. I don't think they gave a specific number.
On Fri, 19 Apr 2024 10:32:48 +0200, Massimo Biancucci <[email protected]> wrote: >Hi everybody, > >In a presentation at GSE I saw a slide with a graph about the advantage of >having more small sysplex LPARs versus a bigger one. >So for instance, it's better to have 5 LPARs with 4 processors than one >with 20. > >There was a sentence: "It doesn't take an extremely large number of CPUs >before a single-image system will deliver less capacity than a sysplex >configuration of two systems, each with half as many CPUs". >And: "In contrast to a multiprocessor, sysplex scaling is near linear. >Adding another system to the sysplex may give you more effective capacity >than adding another CP to an existing system." > >We've been told (IBM Labs, it seems) that a 4 ways DataSharing with 8 CPUs >perform 20% better than a single LPARs with 32 CPUs. >The same (at another customer site) with "having more than 8 CPUs in a >single LPAR is counterproductive". > >Putting these infos all together, it seems it's better to have more small >partitions (how small ???) in data sharing than, let me say, four bigger >ones (in data sharing too). > >Anybody there has direct experience on doing and measuring such scenarios ? >Mainly standard CICS/Batch/DB2 application. >Of course I'm talking about well defined LPARs with High Polarization CPUs, >so don't think about that. > >Could you imagine and share your thoughts (direct experiences would be >better) about where the inefficiency comes from ? >Excluding HW issues (Polarization and so on), could it come from zOS >related inefficiency (WLM queue management) ? >If so, do zIIP CPUs participate in inefficiency growth ? > >I know that the usual response is "it depends", anyway I'm looking for >general guidelines that allow me to choose. > >Thanks a lot in advance for your valuable time. >Max > ><https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> >Privo >di virus.www.avast.com ><https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> ><#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> > >---------------------------------------------------------------------- >For IBM-MAIN subscribe / signoff / archive access instructions, >send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
