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From: Terje Mathisen <terje.mathisen@tmsw.no>
Newsgroups: comp.arch
Subject: Re: what's a mainframe, was is Vax addressing sane today
Date: Fri, 13 Sep 2024 09:15:52 +0200
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Scott Lurndal wrote:
> Lawrence D'Oliveiro <ldo@nz.invalid> writes:
>> On Thu, 12 Sep 2024 02:05:14 -0000 (UTC), John Levine wrote:
>>
>>> They don't just update the software, they swap out entire hardware
>>> subsystems while the overall system keeps running.
>>
>> Xen Orchestra (open-source) can do that on commodity PC hardware.
> 
> The 3leaf hypervisor supported hot-plug memory, hot-plug CPU
> hot-plug PCI 15 years ago with commodity linux guests.

Novell's System Fault Tolerant NetWare 386 (around 1990) supported two 
complete servers acting like one, so that any hardware component could 
fail and the system would keep running, with nothing noticed by the 
clients, even those that were in the middle of an update/write request.

Worked with a private high-speed link between the two servers, so that 
all requests were mirrored from master to slave. This way the slave 
would do the requested operation in sync with the master, maintaining 
the exact same state so it was ready to take over at any point.

BTW, since the pair naturally had separate network connections, they 
could also be connected to separate LAN segments, and this worked 
transparently because every server (single or SFT) maintained a LAN 
segment inside the server: This way the two server connections just 
looked like redundant routing paths.

Terje

-- 
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"