5 ms·

Could someone who has had experience with mainframes explain to me why, in 2020, if I were developing a brand new application with no backwards compatibility ba

Could someone who has had experience with mainframes explain to me why, in 2020, if I were developing a brand new application with no backwards compatibility baggage, what scenarios in which I would want to choose a mainframe rather than a collection of off the shelf servers? Let's assume I have the financial capacity to run my own data center. I'm legitimately curious. I already know how stupid reliable they are in terms of correctness guarantees and staying up when hardware failure and replacement occurs, but what truly sets them apart, considering their cost? At least for we 20-something engineers, I'd wager that nearly all of us have never had an opportunity to be exposed to mainframes.

VonGuard 6y ago
The reliability is a huge thing. Some of the ancient software these things run are the backbones of major systems: Power grids, water systems, air traffic control systems, flight booking systems, weapons controls, or banking systems. Sometimes, these systems are unable to be run in what you'd think about as a traditional distributed systems model. You don't just run that one COBOL program 100 times and kill one process everytime it jams up. The software inside of some of these systems was written in a time when it could be optimized to the absolute bit. At that level of optimization and skill in development, you're not really going to do better or get more throughput with a rewrite. Instead, you just keep wrapping that thing in outer layers and message queues. So, if you need a computer that can absolutely 99.99999% never stop working, including redundant everything (Power, ram, cpu, network) and you're running something that's super old but super efficient and has worked basically perfectly for 30 years, you just buy another one to replace the original, and add some containers into the mix for the queues, or storage adapters or whatever, rather than spend a billion dollars re-engineering the whole thing from scratch as microservices that may or may not work. That, or it's a giant fucking database server. That's usually the case: one big floppy database that runs everything in the company and it's SAP system.
rbanffy 6y ago
IBM can sell you a LinuxONE machine that's mainframe that runs Linux under the z/VM hypervisor. It's probably the biggest Linux server money can buy. And can be carved out into thousands of really nice average servers. You won't have to worry about network components or latency or unreliable servers or anything like that - you can treat it as a data center in a couple racks. Another interesting feature is that they are designed to be monitored, because a traditional business model was to lease a mainframe and rent out capacity to smaller companies that'd pay for things like CPU seconds or bytes read/written.
- aww_dang 6y ago
  Are there any hosting providers offering VMs?
  - lboc 6y ago
    IBM certainly does: http://dtsc.dfw.ibm.com/ http://dtsc.dfw.ibm.com/ They might also know others who do it too. I must admit I've never heard of such a thing from non-IBM sources.
    - rbanffy 6y ago
      The Marist College offers a time-limited z15 Linux on z/VM for free with their LinuxONE Community Cloud project.
galoisgirl 6y ago
When your software handles money. [https://medium.com/selency-tech-product/your-balance-is-0-30000000004-b6f7870bd32e](https://medium.com/selency-tech-product/your-balance-is-0-30000000004-b6f7870bd32e) https://medium.com/selency-tech-product/your-balance-is-0-30... - all those problems are addressed. Also, per [this thread](https://softwareengineering.stackexchange.com/questions/112911/why-the-scorn-for-cobol https://softwareengineering.stackexchange.com/questions/1129...): > In the environments where COBOL thrives, multi-threading is usually left to application containers like CICS or IMS which are good at it, rather, than programmers who tend to be bad at it.

VonGuard 6y ago

The reliability is a huge thing. Some of the ancient software these things run are the backbones of major systems: Power grids, water systems, air traffic control systems, flight booking systems, weapons controls, or banking systems. Sometimes, these systems are unable to be run in what you'd think about as a traditional distributed systems model. You don't just run that one COBOL program 100 times and kill one process everytime it jams up. The software inside of some of these systems was written in a time when it could be optimized to the absolute bit. At that level of optimization and skill in development, you're not really going to do better or get more throughput with a rewrite. Instead, you just keep wrapping that thing in outer layers and message queues. So, if you need a computer that can absolutely 99.99999% never stop working, including redundant everything (Power, ram, cpu, network) and you're running something that's super old but super efficient and has worked basically perfectly for 30 years, you just buy another one to replace the original, and add some containers into the mix for the queues, or storage adapters or whatever, rather than spend a billion dollars re-engineering the whole thing from scratch as microservices that may or may not work. That, or it's a giant fucking database server. That's usually the case: one big floppy database that runs everything in the company and it's SAP system.

rbanffy 6y ago

IBM can sell you a LinuxONE machine that's mainframe that runs Linux under the z/VM hypervisor. It's probably the biggest Linux server money can buy. And can be carved out into thousands of really nice average servers. You won't have to worry about network components or latency or unreliable servers or anything like that - you can treat it as a data center in a couple racks. Another interesting feature is that they are designed to be monitored, because a traditional business model was to lease a mainframe and rent out capacity to smaller companies that'd pay for things like CPU seconds or bytes read/written.

aww_dang 6y ago
Are there any hosting providers offering VMs?
- lboc 6y ago
  IBM certainly does: http://dtsc.dfw.ibm.com/ http://dtsc.dfw.ibm.com/ They might also know others who do it too. I must admit I've never heard of such a thing from non-IBM sources.
  - rbanffy 6y ago
    The Marist College offers a time-limited z15 Linux on z/VM for free with their LinuxONE Community Cloud project.

galoisgirl 6y ago

When your software handles money. [https://medium.com/selency-tech-product/your-balance-is-0-30000000004-b6f7870bd32e](https://medium.com/selency-tech-product/your-balance-is-0-30000000004-b6f7870bd32e) https://medium.com/selency-tech-product/your-balance-is-0-30... - all those problems are addressed. Also, per [this thread](https://softwareengineering.stackexchange.com/questions/112911/why-the-scorn-for-cobol https://softwareengineering.stackexchange.com/questions/1129...): > In the environments where COBOL thrives, multi-threading is usually left to application containers like CICS or IMS which are good at it, rather, than programmers who tend to be bad at it.