RE: availability and resiliency

["Roeland M.J. Meyer" <rmeyer () MHSC com>]

> > Hosts meeting three nines, or better, typically have redundant power
> > supplies and integrated UPS, bootable RAID for the OS, 
> redundant NICs,
> > and SMP CPU configurations.
>
> um...is an smp cpu configuration really going to help your uptime?  or
> are there operating systems or hardware out there that can say to
> themselves "hmph!  cpu 2 seems not to be working correctly...i'd
> better spin it down."

That is a natural function these days. Fail-safe to the "off" state.
Most SMP OS's can recognise when one, out of an SMP CPU set, goes down.

> just for fun a few years back i decided to check if the sun e4000 we
> had had hot-swappable cpus (i figured it didn't, but why not try it?)
> and i pulled one of the boards.  it didn't like it too much.

None of what I claimed is required to be hot-swappable to get 99.9%.
Enough online hot-spares will keep the system up long enough so that you
can replace the entire box. 99.9% allows over 8 hours per year outage.
You should be able to swap out a host in less than 0.5 hours.