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This seems like a good time to ask if there's any point at all to mainframes besides legacy applications. If an org has never used a mainframe before, what wou

This seems like a good time to ask if there's any point at all to mainframes besides legacy applications. If an org has never used a mainframe before, what would be a good reason for them to start?

jcrawfordor 5y ago
If you're processing a very large number of transactions of some kind and require easy to validate complete consistency, mainframes are still generally king. Thus their frequent use in finance and finance-like fields like transactional government services. The throughput for transaction processing can be extremely high due to things like offloaded IO, and mainframe operating systems and development tooling are very amenable to an "if in doubt, back out" approach to consistency (e.g. any failure in processing a batch results in the entire batch being reversed and left for an engineer to troubleshoot). IBM also supports a lot of extreme reliability/consistency use cases like consistency checking through mirrored processing on multiple machines. IBM also likes to argue that, for things like normal Linux VM workloads that require a very high degree of reliability, mainframes can have a lower TCO compared to approaches that rely on complex software for redundancy/failover (mainframes achieve high reliability through hardware-level redundancy, so hardware failures and repairs generally occur without any of the running software ever being interrupted). Judging by the low adoption for this kind of use I'm not sure if it doesn't pan out or it's just too hard of a sell given what's popular in the industry today. There are also more "midcomputer" options for this kind of reliability like HP Tandem and you don't see those as much these days either.
rbanffy 5y ago
Keep in mind you will not find faster single thread performance anywhere else in the computing world. A free VM on the LinuxONE Community cloud puts many developer laptops to shame.
- floatboth 5y ago
  Meanwhile others say "not especially fast for single thread stuff" https://news.ycombinator.com/item?id=28422687 https://news.ycombinator.com/item?id=28422687 I'm pretty sure Apple Firestorm and AMD Zen 3 are trading blows for the best single-thread performance right now depending on workload and optimization. Apple no doubt having the best efficiency due to being on TSMC N5.
  - rbanffy 5y ago
    It depends on the workload, of course. If you are doing things that hit the memory, the massive 960MB L4 of the z15 will help a lot. If all you do fits on the caches of an x86, then the x86 may be a better option. Offloading all the IO to dedicated processors will also be helpful - the z15 feels like it has instantaneous IO. The z15 will probably suck at floating-point SIMD ops (something our laptops are quite good at)
yencabulator 5y ago
x86 is a sports car, it'll go fast for a while, and tends to overheat. Mainframes are freight trains that'll just keep going, pretty much no matter what. They're typically used for the kind of old school business critical stuff where downtime (or errors in output) can cost millions per minute. Imagine hotswapping or upgrading CPUs and RAM without downtime, without having to do any distributed programming. Imagine CPU offload for SQL queries. Imagine fast VM-to-VM TCP connections with hardware offload (direct memory handover) and essentially no CPU cost.

This seems like a good time to ask if there's any point at all to mainframes besides legacy applications. If an org has never used a mainframe before, what would be a good reason for them to start?

jcrawfordor 5y ago

If you're processing a very large number of transactions of some kind and require easy to validate complete consistency, mainframes are still generally king. Thus their frequent use in finance and finance-like fields like transactional government services. The throughput for transaction processing can be extremely high due to things like offloaded IO, and mainframe operating systems and development tooling are very amenable to an "if in doubt, back out" approach to consistency (e.g. any failure in processing a batch results in the entire batch being reversed and left for an engineer to troubleshoot). IBM also supports a lot of extreme reliability/consistency use cases like consistency checking through mirrored processing on multiple machines. IBM also likes to argue that, for things like normal Linux VM workloads that require a very high degree of reliability, mainframes can have a lower TCO compared to approaches that rely on complex software for redundancy/failover (mainframes achieve high reliability through hardware-level redundancy, so hardware failures and repairs generally occur without any of the running software ever being interrupted). Judging by the low adoption for this kind of use I'm not sure if it doesn't pan out or it's just too hard of a sell given what's popular in the industry today. There are also more "midcomputer" options for this kind of reliability like HP Tandem and you don't see those as much these days either.

rbanffy 5y ago

Keep in mind you will not find faster single thread performance anywhere else in the computing world. A free VM on the LinuxONE Community cloud puts many developer laptops to shame.

floatboth 5y ago
Meanwhile others say "not especially fast for single thread stuff" https://news.ycombinator.com/item?id=28422687 https://news.ycombinator.com/item?id=28422687 I'm pretty sure Apple Firestorm and AMD Zen 3 are trading blows for the best single-thread performance right now depending on workload and optimization. Apple no doubt having the best efficiency due to being on TSMC N5.
- rbanffy 5y ago
  It depends on the workload, of course. If you are doing things that hit the memory, the massive 960MB L4 of the z15 will help a lot. If all you do fits on the caches of an x86, then the x86 may be a better option. Offloading all the IO to dedicated processors will also be helpful - the z15 feels like it has instantaneous IO. The z15 will probably suck at floating-point SIMD ops (something our laptops are quite good at)

yencabulator 5y ago

x86 is a sports car, it'll go fast for a while, and tends to overheat. Mainframes are freight trains that'll just keep going, pretty much no matter what. They're typically used for the kind of old school business critical stuff where downtime (or errors in output) can cost millions per minute. Imagine hotswapping or upgrading CPUs and RAM without downtime, without having to do any distributed programming. Imagine CPU offload for SQL queries. Imagine fast VM-to-VM TCP connections with hardware offload (direct memory handover) and essentially no CPU cost.