alt Hacker NewsI'm still hoping to find a more detailed article about modern X86-64 NonStop, complete with Mackie Diagrams.
The last one I can find is for the NonStop Advanced Architecture (on Itanium), with ServetNet. I gather that this was replaced with the NonStop Multicore Architecture (also on Itanium), with Infiniband, and I assume x86-64 is basically the same but on x86-64, but in pseudo big-endian.
A hypervisor (software) approach is one way to accomplish it far cheaper and much more configurable and reusable than having to rely on dedicated hardware. VMware's virtualization method of x86_64 fault tolerant feature runs 2 VMs on different hosts using the lockstep method. Either fails, then the hypervisor moves the (V)IP over with ARP to the running one and spawns another to replace it. More often than not, it's a way to run a critical machine that cannot accept any downtime and cannot otherwise be (re)engineered in a conventional HA manner with other building-blocks. In general, one should never do this and prefer to use always consistent quorum 2 phase commit transactions at the cost of availability or throughput, or eventual consistency through gossip updates at the cost of inconsistency and potential data loss.