The problem with live patching is twofold.

First, you might not reload everything in memory, so it will be patched on disk but not in process.

Second, you have not tested that the system can boot to a functional system. Say you have done live patching for 5 years and never rebooted, and then you have a power loss or hardware failure/upgrade that takes the system down. When you try to bring it back up, it doesn't work. Which configuration change in the past 5 years caused that? Which backup do you use?

And, yeah, everything is hot swappable on VAX. Those machines also cost 6+ figures, and often require a service contract that includes a permanent on site tech.

A Danish bank found out that this can bite you in the ass.

When you hotpatch the system for years then you have no idea if the system can boot up or it will fail somewhere in the booting process.

i.e. you can only trust what you regularly test.

You should't need mainframe for 100% (or five nines if that's fine) service uptime.

You can build that way cheaper with 2-3 proper clustered load balancer units, 2-3 application servers behind those and those using persistent storage (databases,ldap, files) which allow writing multiple nodes simultaneously.

I used to work uni that we had few services from 2012 to 2025 my retirement with zero downtime. One time my manager with tech background tried to add PBR in hurry using WebUI and did not understand cli syntax and caused close to require reboot, but I was able to fix it from cli rolling back previous config and rebooting one unit at time. Upgrading software major version up to each unit supported level wasn't hard, upgrade node it joins back cluster, upgrade another node and it joins cluster, all done. Few times I had to fix manually config for some less important test backend servers that I had forgotten to change before upgrade. No big deal. No major outages during all that 13 years time happened. Some redirecting policy and action syntax was first hard to understand and learn like GeoIP, but I was very surprised how darn reliable and nice they to use and maintain.

The LB's were (Citrix) Netscalers in clustering mode (all nodes process traffic concurrently), which allowed live update one node at time without losing any connectivity through them. That wouldn't have been possible devices in just HA mode.

We had just 2 beefy units which worked very well for us, but you can have 2-32 of them in cluster and managing thousands of servers behind them if you need that. Netscalers are FreeBSD derived where quite a bit of the TCP/IP stack was rewritten adding support many some quite odd features std FreeBSD doesn't have. Much of that is IP/ethernet multicast features, PBR's, Traffic Domains (VRF's) and of many service and monitoring processes which sync cluster (or HA) and if node fails another can continue straight from there without any loss of traffic to clients being proxied.

Though I think most people in this forum are familiar with with haproxy, pound and web-server software provided reverse proxying.

A car analogy if previous were your fancy sport sedan Netscaler and F5 BigIP are formula F1 class cars ie. quite different beasts altogether.

e: And proper LB's are not just for HTTPS etc. but very nice proxying many other protocols were they TCP, UDP or something else. We did done VPN's and something like Cisco AP'S CAPWAP (DTLS ie SSL over UDP). e: typo.

I’ve long wanted that amazing uptime and virtualization and huge I/O and all that cool stuff mainframes offered, but on the desktop or in the closet, with modern CPUs.

I think I’m gonna hafta keep waiting...

> One reason mainframes and micros are still around us, is that you can change almost everything between hardware and software without downtime.

We have some Sun V880s at work and I'm fairly sure the only part you cannot change with the power on and system running is the motherboard itself.

And I would not be surprised if some ex-Sun Gandalf Beard "well akshully"s this comment.