Will dual CPU servers run with one failed?

Do dual CPUs on a modern server actually provide redundancy? If one fails can the server be rebooted and run on the remaining CPU?

In the past I have come across the case where CPU 0 always had to be present so if CPU 1 had failed it would reboot fine but if CPU 0 failed you had to physically swap CPU 1 intyo the cpu 0 socket. I would hope this restriction is no-longer present in modern dual CPU servers but wanted to confirm that.

I have actually been told by HP that dual CPUs do not offer any redundancy because they both have to be present but not sure that is correct.

Solution 1:

Do dual CPUs on a modern server actually provide redundancy?

Yes, they might. For example, Processor Instruction Retry is available on Power systems and is capable of recovering from a failed processor by retrying the instruction that failed during execution, possibly on a different processor.

This isn't available on low end servers such as Intel or AMD, however.

If one fails can the server be rebooted and run on the remaining CPU?

Yes, as long as the server hardware is able to properly detect and recover from the failure. I have a lot of experience with the IBM Intel servers and they are pretty good about recovering from a failed processor and allowing the system to boot from the other socket.

Solution 2:

Do dual CPUs on a modern server actually provide redundancy?

No.

If one fails can the server be rebooted and run on the remaining CPU?

Possible. Depends. If it is dead enough that it is not seen then the Bios may assume only one CPU is in, which may be supported (it mostly is) though yo may loose RAM access (depending on what CPU - some route half the RMA through each CPU).

It alls is depending on how the mOBO handles the situation if a CPU is not there - which is an implemenetation detail.

That said, this is a comically rare case for a CPU to fail in a proper server.