I worked with AIX on Power5/5+ (mid 2000s) and their hypervisor for LPARs and what they called micro-LPARs at the time was astonishingly good. It provided very nice granularity and control for running multiple LPARs. An LPAR is like a VM, but is closer to bare-metal than what you find in an Intel environment. You had to allocate at least 1/10th of a virtual processor per LPAR. They had something called 'entitled capacity' where you could specify the minimum amount of CPU allocation the LPAR would get even if all LPARs running on the same hardware were running 100% busy at the same time.
It all worked exactly as advertised. I was on a small team that did performance monitoring, optimizations, and capacity planning and we watched the metrics very closely for production workloads (running DB2). It was seriously impressive.
I know the industry is full of technical jargon, but IBM is its own universe that pre-dates all of it.
Are LPARs like virtual machines, or like FreeBSD jails (which are like Docker containers, I think)? I get the impression that LPARs are full virtual machines -- each one could be running a different kernel as well as userland.
It's more like virtual machines. You had to use PowerVM, which would take care of virtual I/O, memory, cpu and network. You were able to split in micro partitions and do live partition migrations. In those LPARs you could then use WPARs, which was more like FreeBSD Jails and Solaris Zones. You had two options for it: application wpars and system wpars. I've used AIX[with all hw ecosystem] for many years as a main driver in a bank, and it was ahead of everything else in the market. Still brings good memories - loved it.
100% agree they always have worked in my experience too, still have the pleasure of occasional use of POWER7/8. I always recommended POWER/AIX for reliable compute where budget and s/w compatibility allowed.
I can confirm. I worked at an AIX and Linux shop for about 4 years in the early 2000's. We had a couple of "enterprise" customers who didn't yet trust Linux for their critical applications. It was IBM all the way.
Note, that for that era, AIX was a very solid choice. Only other real option was Sun/Solaris, which was dying after the dot-com implosion.
