Re: what's a mainframe, was is Vax addressing sane today

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"