I've seen NonStop solution failing due to completely mundane reason of insufficient disk space after a burst of transactions. One condition for those 30-year uptimes is also a 100% predictable environment.
Never heard of that one. Funny stuff. Shows even top tier can be improved.
Edit to add: mainframes also run user and server type workloads. Some of those are predictable, some aren't. Bull's virtualize whole desktops. The mainframe as a whole, esp important services, are usually still available despite issues with those. For instance, my company splits stuff between critical on mainframe or AS/400's plus non-critical on whatever is useful ("best-of-breed" they say...). The critical stuff is either on the IBM stuff or leverages it in client-server setup. Those apps either always work or (rarely) they fail-safe in an obvious way that does no damage. Nobody I work with can remember those systems going down over 10 years they worked there. The other stuff regularly has issues across the board. The key difference is effective architecture and how it's implemented.
Edit to add: mainframes also run user and server type workloads. Some of those are predictable, some aren't. Bull's virtualize whole desktops. The mainframe as a whole, esp important services, are usually still available despite issues with those. For instance, my company splits stuff between critical on mainframe or AS/400's plus non-critical on whatever is useful ("best-of-breed" they say...). The critical stuff is either on the IBM stuff or leverages it in client-server setup. Those apps either always work or (rarely) they fail-safe in an obvious way that does no damage. Nobody I work with can remember those systems going down over 10 years they worked there. The other stuff regularly has issues across the board. The key difference is effective architecture and how it's implemented.