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If you have a lot of hardware in the same facility, configured in a way such that you can hotswap and load balance and do all of the other things you might want

If you have a lot of hardware in the same facility, configured in a way such that you can hotswap and load balance and do all of the other things you might want, you only call it a "mainframe" if it's from IBM, who is I believe the only player left in that business. Otherwise, you call it a "server farm", and pretend that it's an entirely different beast. A mainframe (in recent decades) is essentially a proprietary, high cost, tricked out server farm in a box (which is often big enough to be a small building, btw), which might make sense in a few cases but mostly is not as good as a much larger, non-proprietary mainframe, called a "server farm", which is supported by several competing vendors.

zozbot234 6y ago
> Otherwise, you call it a "server farm", and pretend that it's an entirely different beast. Well, server farms don't usually expose a single system image. You can't set the OS to "migrate" workloads seamlessly across hosts the way it can migrate them across CPU cores. Linux is now getting some of the underlying features that are needed to enable this use case, but integrating them into a coherent whole will take some time.
- philsnow 6y ago
  What's the difference between the system image in a huge zOS machine (which, from what I understand supports all kinds of NUMA and hot-pluggable everything, including CPUs, memory, tapes, and disks because they're designed to never, ever need to be shut down) and the cluster "image" provided by a high-availability k8s cluster (which also supports all kinds of hot-pluggable everything)? In a way, the kubelet is the kernel of a k8s cluster. You wouldn't run masters on every node in a cluster, because consensus gets harder quadratically. Maybe workload migration doesn't have to live in the (linux) kernel.
  - zozbot234 6y ago
    Kubernetes is just middleware, it's not a full distributed operating system like, e.g. Amoeba or Inferno. It was never designed from the ground up to expose a meaningful view of the whole cluster to application developers or to those managing the system. As a result of this history, it also features a significant amount of incidental complexity.
mkoubaa 6y ago
The Cray Shasta architecture fits your description of a mainframe

zozbot234 6y ago

> Otherwise, you call it a "server farm", and pretend that it's an entirely different beast. Well, server farms don't usually expose a single system image. You can't set the OS to "migrate" workloads seamlessly across hosts the way it can migrate them across CPU cores. Linux is now getting some of the underlying features that are needed to enable this use case, but integrating them into a coherent whole will take some time.

philsnow 6y ago
What's the difference between the system image in a huge zOS machine (which, from what I understand supports all kinds of NUMA and hot-pluggable everything, including CPUs, memory, tapes, and disks because they're designed to never, ever need to be shut down) and the cluster "image" provided by a high-availability k8s cluster (which also supports all kinds of hot-pluggable everything)? In a way, the kubelet is the kernel of a k8s cluster. You wouldn't run masters on every node in a cluster, because consensus gets harder quadratically. Maybe workload migration doesn't have to live in the (linux) kernel.
- zozbot234 6y ago
  Kubernetes is just middleware, it's not a full distributed operating system like, e.g. Amoeba or Inferno. It was never designed from the ground up to expose a meaningful view of the whole cluster to application developers or to those managing the system. As a result of this history, it also features a significant amount of incidental complexity.

mkoubaa 6y ago

The Cray Shasta architecture fits your description of a mainframe