Comment by technion | Hacker News Reader

Comment by technion | Hacker News Reader

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Regarding the "insert a CD and install software" statement, as someone who hasn't worked on this sort of environment I've always wondered - I have multiple test machines running Windows and Linux. I can push software to a canary installation on an identical server to production. Yes, I can do so indiscriminately, but by the time I push canary to production it's had a certain level of testing.

I knew a mainframe engineer and he certainly didn't have multiple spare mainframes laying around to play with. There might have been some form of partitioned install they called "test" but by the time people bureaucracy gets involved noone is "playing with it" and ergo, there's a lot less actual experts involved.

Bonus question: Was there never a firmware bug that would take down an entire mainframe? A certain server line was advertised with "mainframe like redundancy" on Windows, yet that's exactly my experience.

For test systems, you can create LPARs on IBM z mainframes. I don't have much mainframe experience but I know they have access to test systems and development systems

Not sure about bugs, but I suspect mainframes have fairly redundant software with enough hardware and software to handle unknown bugs.

Or VMs (guests) in z/VM. The guest OS can be linux, CMS, z/OS, z/VM (2nd level), etc.

I believe you can stack z/VM as deep as you like. Current x86s can do that too, AFAIK.

> Was there never a firmware bug that would take down an entire mainframe?

Yes, there was quite an ugly one not that long ago in fact. A local mega-corporation which still has some mainframes had its main (and redundant) systems just roll over and die suddenly, plus their hot backup systems which were offsite. I don't remember all of the details, but IIRC this was a case of "We [the vendor] knew we had a major bug, and we had a fix for it, but we were remiss about getting it out to all of our customers in a timely manner." This type of thing is shockingly rare in the mainframe world, though.

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